IOC-UNEP-WMO-SAREC Planning Workshop on An Integrated ...

Intergovernmental Oceanographic Commission<strong>Workshop</strong> Report No. 96 - Supplement 1<strong>IOC</strong>-<strong>UNEP</strong>-<strong>WMO</strong>-<strong>SAREC</strong><strong>Planning</strong> <strong>Workshop</strong> on An IntegratedApproach to Coastal Erosion, SeaLevel Changes and Their ImpactsInstitute of Marine Sciences (University of Dar es Salaam)Zanzibar, United Republic of Tanzania, 17-21 January 1994Submitted Papers1. Coastal ErosionUNESCO

TABLE OF CONTENTS<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page (i)I. INTRODUCTION: REVIEW OF COASTAL EROSION PROBLEMS IN THE WESTERNINDIAN OCEAN REGION ..................................................... 11. COASTAL EROSION PROBLEMS ............................................ 11.1 COASTAL EROSION PROBLEMS: IN RELATION TOGEOGRAPHICAL AREAS .............................................. 11.2 COASTAL EROSION PROBLEMS: A CAPACITY PROBLEM .............. 11.3 COASTAL EROSION PROBLEMS: AN INTERDISCIPLINARYPROBLEM TOWARDS ICZM ............................................ 11.4 COASTAL EROSION PROBLEMS: CLEAR DEFINITIONS ................ 21.5 COASTAL EROSION PROBLEMS: SUMMARY ......................... 22. GOALS ................................................................... 2ANNEX: REFERENCES ....................................................... 2II.NATIONAL REPORT: STATUS OF COASTLINE CHANGES IN KENYA AND ITSIMPLICATIONS ON SUSTAINABLE COASTAL ZONE DEVELOPMENT ANDMANAGEMENT ............................................................. 41. INTRODUCTION .......................................................... 42. HISTORY OF COASTAL ZONE DEVELOPMENT ............................... 43. MAJOR SHORE GEOTYPES ................................................. 73.1 THE NORTHERN SECTOR .......................................... 73.2 SOUTHERN SECTOR ............................................... 74. COASTAL EROSION ....................................................... 75. ANTHROPOGENIC CONTRIBUTION TO SHORELINE CHANGE .................. 86. ATTEMPTS AT EROSION CONTROL ......................................... 86.1 SUITABILITY OF SEA WALLS IN EROSION MITIGATION FORTHE KENYA CASE .................................................... 97. THE ROLE OF THE CURRENT DEVELOPMENT STRATEGY ON LONG TERMSOCIO/ECONOMIC IMPACT OF COASTAL EROSION ....................... 98. AVAILABLE DATA ON COASTAL EROSION .................................. 98.1 INVENTORY ...................................................... 98.2 MONITORING .................................................... 118.3 INFORMATION ON GEOLOGY ...................................... 118.4 MAPS, BATHYMETRIC CHARTS AND AERIAL PHOTOGRAPHS .......... 118.5 HISTORICAL INFORMATION ....................................... 119. NATIONAL POLICY ON COASTAL EROSION .................................. 1110. LAND USE PLANNING AND RELATED LEGISLATION ......................... 1210.1 LAND POLICY ................................................... 1210.2 CATEGORIES OF LAND ........................................... 1210.3 USE AND DEVELOPMENT OF LAND ................................ 1210.4 RELEVANCE OF THE CURRENT LAND USE POLICY ON COASTALEROSION ..................................................... 1310.5 EXPLOITATION OF MARINE SAND ................................. 1310.6 EXPLOITATION OF REEF ROCK .................................... 1311. PROBLEM RELATED TO LAND USE PLANNING AND COASTAL EROSION ..... 1312. MANGROVE MANAGEMENT POLICY ....................................... 1313. COASTAL ZONE PLANNING DEVELOPMENT AND MANAGEMENT POLICY ...... 1314. DISCUSSION ............................................................. 14ANNEX I: REFERENCES ..................................................... 14ANNEX II: LISTS OF SCIENTISTS INVOLVED IN COASTAL EROSION STUDIES INKENYA .............................................................. 16III. COASTAL EROSION IN KENYA : A CASE STUDY OF THE MOMBASA DIANI AREA .. 171. INTRODUCTION .......................................................... 171.1 STUDY OBJECTIVES ............................................... 171.2 STUDY AREA ..................................................... 171.3 GEOLOGICAL SETTING ............................................ 172. RESULTS ON MORPHOLOGY ............................................... 172.1 MAJOR MORPHOLOGICAL FEATURES ............................... 173. COASTAL ZONE MANAGEMENT ........................................... 23

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page (ii)4. COASTAL PROTECTION MEASURES ........................................ 235. RECOMMENDATIONS ..................................................... 28ANNEX: REFERENCES ....................................................... 28IV. STATUS OF COASTLINE CHANGES IN MAURITIUS .............................. 291. PHYSICAL ENVIRONMENT ................................................. 291.1 GEOGRAPHICAL SETTING ......................................... 291.2 THE COASTAL ZONE .............................................. 291.3 ENVIRONMENTAL PARAMETERS ................................... 351.4 TIDAL WAVES .................................................... 402. EROSIONAL SITES ........................................................ 402.1 GENERAL ........................................................ 402.2 CELL A (ROCHES NOIRES TO CAP MALHEUREUX) .................... 412.3 CELL B (CAP MALHEUREUX TO FLIC EN FLAC) ...................... 412.4 CELL C (FLIC EN FLAC TO LE MORNE) .............................. 442.5 CELL D (LE MORNE TO MAHEBOURG) ............................... 442.6 CELL E (MAHEBOURG TO ROCHES NOIRES) ......................... 443. FACTORS CONTRIBUTING TO SHORELINE CHANGES ......................... 453.1 NATURAL PHENOMENA ..................... 453.2 ANTHROPOGENIC FACTORS ....................................... 474. EFFECTS OF SHORELINE CHANGES ......................................... 504.1 AGRICULTURE ................................................... 504.2 STRUCTURES ..................................................... 504.3 TOURISM ........................................................ 504.4 AQUIFER ......................................................... 504.5 CHANGE IN ECOSYSTEM .......................................... 504.6 SAND MINING .................................................... 514.7 SALT INDUSTRY .................................................. 534.8 COASTAL INDUSTRIES ............................................ 534.9 HARBOUR INFRASTRUCTURE AND SERVICES ........................ 534.10 SALINE INTRUSION ............................................... 534.11 COASTAL WATER POLLUTION ..................................... 535. CONTROLLED MEASURES ................................................. 545.1 PHYSICAL CONTROL .............................................. 545.2 PLANNING CONTROL ............................................. 566. RATE OF SHORELINE AND BATHYMETRIC CHANGES ......................... 567. NATIONAL POLICY ON COASTAL EROSION .................................. 607.1 PLANNING CONTROL ............................................. 607.2 SETBACK ........................................................ 607.3 ENVIRONMENTAL IMPACT ASSESSMENT ........................... 617.4 ENVIRONMENT SENSITIVE AREAS .................................. 617.5 POLLUTION FROM LAND BASED SOURCES .......................... 617.6 NATIONAL COASTAL EROSION RESEARCH STRATEGY ............... 62ANNEX I: REFERENCES ...................................................... 62V. SEYCHELLES NATIONAL REPORT COASTAL EROSION, SEA-LEVEL CHANGES ANDTHEIR IMPACTS ............................................................. 641. SEYCHELLES: BASIC INFORMATION ........................................ 642. COASTAL GEOMORPHOLOGY AND CLIMATE BASELINE ...................... 643. COASTAL ECOLOGY AND SHORELINE CHANGE ............................. 654. COASTAL PROCESSES IMPACTING ON EROSION ............................. 654.1 WATER MOVEMENT .............................................. 664.2 NEAR SHORE WATER-BORNE SEDIMENT ............................ 664.3 AEOLINA TRANSPORT ............................................. 664.4 APPLICATION OF PHYSICAL COASTAL PROCESSES ................... 665. PROBLEM AREAS IN RELATION TO COASTLINE CHANGE ..................... 676. CLIMATE CHANGE AND SEA-LEVEL RISE7. ANTHROPOGENIC EFFECTS AND SHORELINE CHANGE ................ 687.1 SAND EXTRACTION ............................................... 687.2 DESTRUCTION OF PROTECTIVE CORAL REEF SYSTEMS ANDCORAL BARRIERS .................................................... 68

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page (iv)3.2 MAZIWI ISLAND OFF PANGANI (TANGA) ............................ 873.3 COASTLINE CHANGES ALONG KUNDUCHI BEACH, NORTH OF DAR ESSALAAM ............................................................ 884. COASTAL EROSION IN ZANZIBAR .......................................... 924.1 FISHING ......................................................... 924.2 BEACH SAND MINING AND QUARRYING ............................ 924.3 MANGROVE CUTTINGS ........................................... 934.4 MAGNITUDE OF EROSION ......................................... 935. SUMMARY, DISCUSSION AND CONCLUSIONS ............................... 945.1 OBVIOUS RECOGNITION OF COASTAL EROSION ..................... 945.2 REASONS FOR COASTAL EROSION IN TANZANIA .................... 945.3 MEASURES TAKEN ................................................ 955.4 NATIONAL LEGISLATION ON COASTAL EROSION .................... 955.5 ESTABLISHMENT OF COASTAL INVENTORY ......................... 975.6.OTHER RECOMMENDATIONS ................................ 97ANNEX I: REFERENCES ...................................................... 97VII. BEACH EROSION NORTH OF DAR ES SALAAM ................................ 1071. INTRODUCTION ......................................................... 1072. MATERIALS AND METHODS .............................................. 1072.1 WIND ........................................................... 1072.2 WAVES ......................................................... 1072.3 CURRENTS ...................................................... 1083. RESULTS ............................................................... 1084. DISCUSSION ............................................................ 110ANNEX I: REFERENCES ..................................................... 111VIII. LITTORAL SEDIMENT MANAGEMENT ........................................ 1231. LITTORAL SEDIMENT MANAGEMENT ..................................... 1231.1 INTRODUCTION ................................................. 1231.2 SHORE MORPHOLOGY CLASSIFICATION FOR THE GREATLAKES ............................................................. 1231.3 LITTORAL CELL BASICS ......................................... 1251.4 LITTORAL PROCESSES .......................................... 1261.5 BEACH PROFILES ................................................ 1281.6 SEDIMENT TRANSPORT MODELLING .............................. 129ANNEX I: REFERENCES ..................................................... 137IX.REGIONAL. ASPECTS OF COASTAL EROSION IN WEST AFRICA - THE CASE OF THEBIGHT OF BENIN ........................................................... 165ABSTRACT ................................................................ 1651. INTRODUCTION ........................................................ 1652. GENERAL DESCRIPTION OF THE BIGHT OF BENIN ........................... 1653. CLIMATE ............................................................... 1674. HYDROLOGY ........................................................... 1675. OCEANOLOGY .......................................................... 1676. GENERAL COASTAL CONDITIONS ........................................ 1687. THE ROCKY COASTS .................................................... 1688. THE SANDY COASTS .................................................... 1689. THE DELTA COASTS .................................................... 17010. CAUSES OF EROSION IN THE BIGHT OF BENIN ............................ 17011. COASTAL PROTECTION IN THE BIGHT OF BENIN ......................... 17112. THE FUTURE DIRECTION OF COASTAL EROSION CONTROL IN THE BIGHT.. 172ANNEX: REFERENCES ..................................................... 173

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 1I. INTRODUCTION: REVIEW OF COASTAL EROSIONPROBLEMS IN THE WESTERN INDIAN OCEAN REGIONby A. GranlundThe intention with this paper is to give a short review of the status of Coastal Erosion Problems notedin the Western Indian Ocean, and raise some issues that could be discussed during the workshop. Thephenomena of Coastal Erosion have been ongoing since the forming of the Oceans. Thus, the Man drivenCoastal Erosion has accelerated erosion on several places in the Coastal Zone.Sediment transportation is a process that has been active throughout the geological history. Thedynamic development of coastal areas is affected by several well-known physical factors. To fully understandsea-level fluctuations and coastal erosion it is also important to have good knowledge about the presentgeological development for various coastal environments.Important factors such as active subsidence over basin areas can result in "sea-level rise" and changethe oceanographic conditions in a long term perspective. The continental drift is one of the important factorsto understand and interpret the fundamental processes that govern the sedimentation processes.It is difficult to predict the future without knowing the past. It is therefore highly important to buildup baseline studies, as accurate as possible, over coastal erosion areas of special interest. In these efforts alldifferent aspects should be considered and integrated. It is also important to differentiate between Man madecoastal erosion and coastal erosion caused by natural processes in the environment.1. COASTAL EROSION PROBLEMS1.1 COASTAL EROSION PROBLEMS: IN RELATION TO GEOGRAPHICAL AREASThe Intergovernmental Oceanographic Commission (<strong>IOC</strong>) did an "Outline of the project proposalon Coastal Erosion in the Western Indian Ocean Region - Scientific Appraisal and Management"(<strong>IOC</strong>/INF-914). In this report the <strong>IOC</strong> consultant describes several areas in the Western Indian Ocean, whereCoastal Erosion has been severe. The erosion problems are concentrated to the coral-fringed coasts in theregion. In Tanzania, areas north and south of Dar-es-Salaam, on Zanzibar and Pemba Islands have severecoastal erosion. In Kenya Coastal Erosion appear to be severe both north and south of Mombasa. In theSeychelles coastal erosion has been detected on the islands of La Digue, Bird Island and Praslin. The <strong>IOC</strong>report also states that various attempts have been made in all these countries to protect the coasts from furthererosion but few such attempts have achieved anything beyond temporary relief.1.2 COASTAL EROSION PROBLEMS: A CAPACITY PROBLEMA major problem in solving the coastal erosion is the lack of baseline studies. These baseline studiescan never be achieved without expansion of training components. It is therefore important to provide regionalresearch and training activities, which will facilitate the provision and exchange of information The coastalerosion problems need to he solved regionally, with local expertise, and with some minor exchange withvisiting experts. The goal is to build up a carrying capacity of local experts dealing with coastal erosionproblems.1.3 COASTAL EROSION PROBLEMS: AN INTERDISCIPLINARY PROBLEM TOWARDS ICZMThe Coastal Erosion Problems are of various sources, man driven or natural. To understand the Mandriven coastal erosion problems an interdisciplinary view of the problem is needed. It has been described bymany experts (e.g. Odada ) that Integrated Coastal Zone Management (lCZM) will be the

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 2vehicle that could solve the problem of man generated coastal erosion. To achieve a sustainable marinecoastal environment, with a clear understand of the man generated processes, an interdisciplinary strategyis needed. A combination of physical oceanographers, marine biologists, marine geologists together withsociologists and economists should make up the interdisciplinary platform.1.4 COASTAL EROSION PROBLEMS: CLEAR DEFINITIONSOne of the major problems in the interpretation work of Coastal Erosion is the definition of the wordCoastal Erosion. Much effort must be emphasized to define and describe the difference between Man drivenCoastal Erosion and Natural Coastal Erosion.1.5 COASTAL EROSION PROBLEMS: SUMMARYThe report "Outline of the project proposal on Coastal Erosion in the Western Indian Ocean Region- Scientific Appraisal and Management" (<strong>IOC</strong>/INF-914) was discussed during the <strong>IOC</strong> Regional Committeefor the Cooperative Investigation in the North and Central Western Indian Ocean, Third Session, held onMauritius 14-18 December 1992. The recommendations thought that the report was little biased towardsgeology driven problems concerning coastal erosion, and that effort also should be done in areas like socialscience and disciplines which lies in line with ICZM. It was said that the <strong>IOC</strong> Coastal Erosion workshopshould be the start of the integrated regional work in this field.Several scientists in the East African region have proposed papers on Coastal Erosion. The <strong>IOC</strong>workshop should actively try to incorporate them in the future work.The workshop will have a unique opportunity to combine sea level rise problematic with coastalerosion problems.2. GOALSissues;The outcome from the regional workshop could give a better understanding of some of the following- To be able to differentiate between Man made Coastal Erosion and Natural Coastal Erosion in orderto create an acceptance of Natural Coastal Erosion- The country profiles generated for the workshop are very important in setting up baseline studies.The country profiles need to be carefully compared at the workshop for identification of mutualproblems etc.- To set up baseline studies is important on order to create a platform for ground truth data- With establishment of baseline studies in selected areas the base for good monitoring systems to beused for possible coastal erosion predictions is set.- The solution to Coastal Erosion Problems and also Sea-level problems should preferably be solvedin an integrated program with a stepwise goal seeking method.- The generated information from the integrated regional work should be incorporated in an integrateddatabase for local, regional and global use in solving Coastal Erosion ProblemsANNEXREFERENCES"Outline of the project proposal on Coastal Erosion in the Western Indian Ocean Region - ScientificAppraisal and Management" (<strong>IOC</strong>/INF-914) (R.S. Arthurton)<strong>IOC</strong> <strong>Workshop</strong> Report No. 77. <strong>IOC</strong>-<strong>SAREC</strong>-KMFRI. Regional <strong>Workshop</strong> on Causes and Consequences ofSea-Level Changes on the Western Indian Ocean Coasts and Islands (Mombasa, Kenya, 24 - 28 June 1991)<strong>IOC</strong> Manual and Guides No 14. Vol I and 2. Manual on Sea-level Interpretation and Analysis.

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 3<strong>IOC</strong> Regional Committee for the Co-operative Investigation in the North and Central Western Indian Ocean,Third Session, Vacoas Mauritius, 14-18 December 1992.Background paper for the <strong>SAREC</strong>/FAO/<strong>IOC</strong>/SIDA/<strong>UNEP</strong>/WORLD BANK workshop on integrated coastalzone management in East Africa - April 20-23 Arusha 1993. Coastal Erosion and Flooding in East Africa.Eric Odada.

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 4II.NATIONAL REPORT: STATUS OF COASTLINE CHANGES INKENYA AND ITS IMPLICATIONS ON SUSTAINABL ECOASTAL ZONE DEVELOPMENT AND MANAGEMENTBy Dr. E. Okemwa, Mr. K. Kairu, Mr. T. Munyao1. INTRODUCTIONThe Kenya coastal zone extends from about 4 30'S to 4 35'N and has a total shoreline length of over480km. From a geological perspective, the coastal zone may be extended to include the Kenya continentalmargin. This zone can be divided into three distinct physiographic provinces (fig. 1), defined on the basisof Litho-stratigraphic units. Moving from the east to west, the coastal plain which is the first physiographicunit, rises from sea level datum(OD) to over 200m, the foot plateau extends from an elevation of 200m ODto 500m OD and the Nyika at above 500m OD.The coastal plain is the most important physiographic province in relation to coastline change. Thenear surface geology in this sector evolved in Post Miocene times on the sub-Miocene erosion bevel. Thegeologic evolution of this province has been influenced strongly by the relative change in sea level, theMiocene and Pleistocene erosion bevels, the reef systems and the major drainage patterns. These elementshave strongly controlled to different extent the erosional and depositional cycles of the Quaternary and recentstratigraphy and evolution of the present shore configuration.The coastal zone which is vulnerable to change can confidently be assumed to conform to the coastalplain for this study. Two distinct shore types are observed within this physiographic province. The northernsector, which shows accretional trends in Holocene times and the southern sector, which has been dominatedby erosion trends at least during the Holocene. The two distinct shore types, however, exhibit whereverpreserved, a similar series of fossil sea level terraces first described in Mombasa area (Rais Asa, 1978) andobserved all along the coast by the authors. For coastal zone management, the terrace complexes can begrouped into four levels that can easily be recognized in the field unless obscured by the drift geology. LevelI comprises of terraces at 0-5m OD elevation, level II at the 5-10m OD elevation, level III at the 10-25m ODelevation and level IV, all terraces above 25m OD. These levels constitute very important geological subenvironmentsin terms of coastal zone development and have a strong significance on the susceptibility ofthe coastal environments to coastal erosion.2. HISTORY OF COASTAL ZONE DEVELOPMENTLike in many world coastal nations, the earliest permanent settlements in Kenya developed along thecoastal zone. Maritime trade and easy communications provided by the water ways were some of the mostimportant driving forces in the establishment of this settlements.Most of the old settlement therefore evolved next to favorable natural ports. Among the mostimportant settlements observed today that date back to between 8th and 18th century include, Manda, Pate,Lamu Shanga, Omwe and Kiunga in the Lamu area; Ungwana, Mambrui and Malindi in Malindi area; andMombasa, Mtwapa, Vumba Kuu in Mombasa area. Mombasa, Malindi and part of Lamu are located on levelII environments and above and the lower parts of Lamu, and Kipini are on level I (fig.2). Due to the genericrelationship between good drainage channels and relatively stable coastal geology at least in quaternary, mostof these old settlements that have survived the impact of coastal processes were located on limestone terrain(fig.2). Evidence of drowned ports occur in several localities like Lamu and Ungwana bay areas. Theserepresent settlements that were located on the more dynamic environments of the coastal zone. Up to the mid20th century, settlement expansion occurred on the existing towns especially Lamu, Mambrui, Malindi andMombasa.In the last three decades, Kenya coastal zone development has transformed from trade, to serviceoriented industry for the tourism industry. This new industry requires beautiful low lying coastalenvironments comprising of unconsolidated sand deposits (the beaches) (fig.2). Unlike the old sites, these

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<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 7new sites are relatively mobile geological environments, characterized by annual and longterm shorelinetransformations, a fact that was not appreciated by most of the coastal zone developers. The most preferredsites are level I and II environments (fig.2). From our studies, Diani, shelly beach, Nyali, Bamburi,Kikambala Watamu and Malindi coastal tourist centers are located on level I and II environments. A goodexception is the Nyali site where development was limited to level II by geological control. As a result, amassive investment of national economic importance is sited in areas that are experiencing erosion or aresusceptible to erosion. This trend of coastal development will strongly influence the magnitude of the impactof coastal erosion on different settlements on the longterm.3. MAJOR SHORE GEOTYPES3.1 THE NORTHERN SECTORThe northern sector extends from slightly north of Malindi to the Lamu archipelago and falls withinthe area of the present and pre-historic Tana and Sabaki deltaic systems. Levels I and II terraces areextensive and reach a maximum width of over 40km. In most of the area they are obscured by the accretionof quaternary unconsolidated deposits. These are represented by deltaic sands, clays, wind blown sands andlagoonal deposits. In Ungwana bay, barrier island systems associated with fossil drainage patterns formimportant coastal elements. This sector is dominated by secondary shorelines comprising Pleistocene torecent unconsolidated environmental rock units. Due to the deltaic setting, major sectors of this coastal areaextending to over 10-40km lie only a few meters above the highest spring tide. This increases vulnerabilityto flooding. Most of the near surface sequences of this area are unconsolidated and are therefore readilyreworked by the active coastal processes.3.2 SOUTHERN SECTORThis sector extends from the Tanzania border to the Malindi area. The sector encompasses the areaof Pleistocene to recent reef proliferation. The area is therefore dominated by coral reef limestone andcoquinoid limestone units that show good cementation. The near surface diagenesis of carbonates undernormal temperature and pressure has produced the stable Pleistocene to recent topography with a positiverelief that has survived during periods of frequent changes in sea level. This is evidenced by numerous relictfeatures of raised sea level terraces, that formed important Pleistocene and Holocene depositionalenvironments defined as level I to IV. The drift geology on terraces lower than 13m rarely exceeds 3m inthickness. However, Holocene accumulation on some of the lower level I terraces with favorable conditionshave evolved into littoral cells that comprise some of the most sought after coastal environments for hotel andresidential development. During the Holocene, this area has experienced gradual erosion.4. COASTAL EROSIONCoastal erosion work was first initiated in 1987. The first step involved taking an inventory of theerosion problem. Later in 1988 and 1989, sites for monitoring coastal erosion were selected in Diani,Bamburi, Mambrui and Ngomeni. In 1990, a review of erosion inventory data indicated that coastal erosionwas widespread and affected both developed and undeveloped low lying coastal environments. It wasrealized that coastal erosion monitoring alone could not provide quickly a reliable data base unless undertakenon a longterm basis due to the numerous forcing factors. It was also realized that the current rapid coastalzone development cannot wait until reliable data was collected. An urgent need to formulate guidelines forcoastal developers required formulation of reasonably acceptable method of forecasting longterm shoremovement especially for site evaluation for development. Such evaluation should consider factors that affectcoastal sediment budgets and changes in the relative sea level stand. From this consideration, coastal erosionresearch began to also focus, in addition to monitoring, the study of environmental geology as a tool forforecasting the susceptibility of shorelines to predetermined changes in sea level and sediment budget. Areport on this is being prepared covering a large section of the coastal zone. In the current proposal emphasisis also placed on coastal hydrodynamics.4.1 OBSERVED EROSION TRENDS

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 8From erosion inventory, erosion features have been observed all along the coast on both the twoshore geotypes. Shoreline retreat is however a more serious problem on the primary shorelines of thesouthern sector on both developed and virgin areas. A survey of the distribution also shows that most of theaffected coastal environments include those that evolved through the deposition of unconsolidated Quaternaryand recent deposits on level I environments. These comprise very limited but important environments in thesouthern sector where they rarely exceed 500m.5. ANTHROPOGENIC CONTRIBUTION TO SHORELINE CHANGEAnalysis of the relative contribution by the different forcing factors of coastal erosion has receivedonly limited attention. Munyao (1992) while carrying out studies on sedimentology of Shirazi-Funzi lagoonabout 70km south of Mombasa, observed that mangrove exploitation at the edges of the mangrove forest, orwhere a narrow cover of mangrove tress occur along the coastline exposes the shoreline to waves andcurrents, allowing erosion to occur. This problem, for example, is evident along the Funzi Island shorelinewhere structures built near the high water mark have been damaged due to erosion.From the available evidence of erosion inventory on sediment budgets, local geology and assessmentof the erosion distribution, areas where anthropogenic contributions may have played an important role inshoreline change can be identified.In addition to the above mentioned, areas with pronounced erosion dueto the added anthropogenic contribution include, the extensive areas of beach recreational facilities, fish andmangrove landing areas. This may be attributed to interference with normal beach berm and dune evolution.The northern sector comprise shorelines whose sediment budgets are very dependant on the Tana and Sabaki9 3 -1 8 3 -1river's contribution, both with an average annual water discharge of over 5.54 x 10 m yr and 4.71 x 10 m yrrespectively.Since 1937 when the first bathymetric chart of the Malindi area was drawn, accretion of both theSabaki and Tana deltas has been recorded, deflecting the shoreline at the delta front by over 300m in the caseof the Sabaki. Data on the Tana is not available though evidence of accretion is observed in the coastal form.At the end of the 18th century, the Tana was diverted to a more northerly course along the Ozi channel fromits relict mouth in the mid Ungwana bay area. In the last two decades, major dam construction and irrigationschemes have affected the Tana. This may limit sediment discharge by the river significantly. Extensiveagriculture from 19th century and associated erosion of top soil must have resulted in an increase in the riversediment load. However, recent dam construction must have limited inflow of these sediments to the Indianocean. On the longterm, this negative sediment budget may result in an increase in coastal erosion on theseriver dependant coastal systems. The current erosion trends observed south of Ungwana bay where Holocenedeposits are being reworked may be due to the natural channel switching observed for the Tana estuary, theconstruction of the Ozi channel, or the new dam construction. Increased water shed area agriculture in theSabaki catchment has had a positive impact on the coastal sediment budget for the case of the Sabaki andprobably the Malindi bay where most of these sediments are restricted.In the southern sector, the most developed area, primary and secondary anthropogenic impacts areobserved. Primary impacts include destruction of shoreline vegetation and flattening of the natural beachberm during development and continuous trampling of any new dune development. Secondary impactsinclude the construction of sea walls as erosion control structures. These have resulted in migration of beachsands and degradation of beaches of this sector (fig. 3). In the extensively protected areas, normal beachprofiles which always have a beach face exposed at high water have disappeared. Coastal protectionespecially sea walls are therefore a major threat to the beach resource.6. ATTEMPTS AT EROSION CONTROLThere are numerous examples of individual attempts by coastal developers to control coastal erosion.Extensive coastal protection structures are observed in Diani, Shelly beach, Bamburi, Kikambala and SilverSands areas (fig. 1). In all these areas, no unified sectorial approach at coastal protection has beenundertaken. Sea walls and rabble lines which are practical in cases of individual approach to shore protectionhave been the most preferred coastal defense strategies. The design of the current defense structures is basedon wave refraction and reflection. This demands that the structures be robust, with a foundation protectedby amour rock from toe erosion. Apart from very few localities, these considerations were ignored either due

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 9to aesthetic reasons or lack of know how. These two factors alone have resulted in the repeated failure andcollapse of most of the coastal erosion defense initiatives.6.1 SUITABILITY OF SEA WALLS IN EROSION MITIGATION FOR THE KENYA CASEOur surveys show that sea walls actually stop shoreline retreat. Their effectiveness can be explainedon the basis of the local geology which provides good foundation because the thickness of the drift geologyrarely exceeds 3m. However, the aim in the Kenyan case is not only to stop shoreline retreat, conserving ofthe beach sands is a primary priority. Since sea walls are by design both wave refractive and reflectivestructures, they interfere with beach evolution and result in massive sand migration leading to beachdegradation infront of the protected areas (fig. 3a). This is a problem of concern in Diani and Bamburi areas.where Wall-edge erosion in the adjacent unprotected areas (fig. 3b) associated with coastal defense structuresis a major cause of erosion protection proliferation. The sea walls and rabble lines interfere with the qualityof the beach, the main resource influencing site selection for the tourism based infrastructure. This factorexcludes sea walls from suitable structures for erosion protection. It is therefore important that alternativemeasures that would have limited impact on the natural beach evolution and at the same time retain theaesthetics of the beaches be sought.From considerations of the geologic evolution of the natural environments forming the major touristbeach centers now suffering from erosion, which comprise wide and small coral cays that have evolved inbetween headlands behind wide nearshore platforms, a sectorial approach to coastal erosion protection,utilizing a combination of detached offshore breakers and groynes can be utilized to limit the amount ofenergy reaching the shore and limit longshore sand migration. These two factors may positively influencethe preservation of the limited beach environments observed today on the fossil terrace in this sector.7. THE ROLE OF THE CURRENT DEVELOPMENT STRATEGY ON LONG TERMSOCIO/ECONOMIC IMPACT OF COASTAL EROSIONOur field surveys have shown that coastal erosion is dominant in the level I environments. Level IIenvironments are affected to a very small degree. In most parts of the area on the developed southern sector,level I environments constitute 20-300m of the shore front. Actual construction could have been limited tolevel II. This alone could have put most of the infrastructure beyond reach of the current erosion problem.In this regard, its quite clear that bad site selection has increased the vulnerability of many of the coastaldevelopments to erosion. The current need for expensive coastal defense structures for the alreadyestablished massive investment along the coastal zone could have been avoided.8. AVAILABLE DATA ON COASTAL EROSIONAn erosion inventory and establishment of monitoring stations was initiated in 1987/1991. The initialproject was later expanded to include other aspects of environmental geology. The area covered by thesestudies include sectors of the coast from the central Ungwana bay in the northern sector to the Shimoni areain the south. The areas to the north of Lamu and south of Shimoni have been ignored due to limited funding.8.1 INVENTORYField excursions to selected representative sites on the basis of experience and desk studies wereundertaken in the described shorelines in 1987-1991. The coastal morphology, general texture andcomposition of the major geological elements, and shore morphology were recorded. Evidence of erosionwas analyzed by referencing to shore attributes like buildings, reworking of stabilized deposits with terrestrialvegetation or established coconut plantations. This data base has now been compiled to provide informationon the general erosion trends.

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<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 118.2 MONITORINGMonitoring stations were first established from 1988-1990 in different areas. Two methods ofmonitoring were used. Initially the method utilized fixed poles or established shore reference structures andphotography to form an indication on the movement of a selected shore elements. Levelling using anengineers level was utilized from late 1991. For this, discrete bench marks were established. This methodis described by Ibe & Quelennec (1989). Referenced stations are therefore available from 1991 in someareas. However, evidence on the general direction of shore movement is available from 1987 inventory.Available evidence points out strongly that major shorelines have been retreating during 1987-1992 period,but for the time being, one cannot give an exact erosion rate due to the short period and complex cyclicbehavior of shorelines. Ngomeni, one of the areas with the fastest erosion rates, an average retreat of over0.5m per year has been calculated. In the rest of the area the rate is lower.8.3 INFORMATION ON GEOLOGYExtensive information on the geology is available. This is represented for the Kwale, Mombasa,Mazeras, Kilifi, Malindi and Fundi isa areas by geological reports (Geol. Surv. Kenya Report No. 24, 34, 36and 52). The northern sector is poorly covered.8.4 MAPS, BATHYMETRIC CHARTS AND AERIAL PHOTOGRAPHSThe area is covered by several series of maps and bathymetric charts. The oldest bathymetric chartsdate back to 1937. These were updated in 1950's and 1980's. The scale varies from 1:12,000 to 1:1,000,000.Topographic maps cover only recent work with only a few areas with old topographic maps. Air photographsat various scales 1:12,000 or 1:5000 are available for the different sectors of the coastal zone. The seriesavailable does not cover the whole coast continuously, this includes a 1937, 1953 and 1982 series.8.5 HISTORICAL INFORMATIONInterview of local authority personnel, coastal developers and retired administration managers of thefew Coastal Erosion Defence Works in Malindi and Lamu and people with residential houses along theshoreline give good indication on longterm coastal erosion trends for the respective areas. A few books andreports and archeological studies (Wilson, 1992) have useful historical information. A slow shoreline retreatis supported by analysis of the historical information.9. NATIONAL POLICY ON COASTAL EROSIONCoastal erosion in the minds of many people in Kenya is a relatively new environmental problem thatcame into the limelight only in the last ten years, and got significant attention as an environmental problemneeding special attention in the last three years. As a result no major policy considerations have been initiatedspecifically to deal with the problem. However, sustainable development, good environment managementassociated with environmental impact assessment before any project is initiated has been emphasized as afundamental issue in the development policy in the current development plan (1988 - 1993).Kenya Marine and Fisheries Research Institute was established by the government to play anadvisory role on policy issues related to the management of marine resources. To achieve this, the institutewas given a mandate covering all aspects of marine and fresh water research. Coastal erosion falls withinthe physical and geological oceanographic area of the mandate. The institute has already initiated a projectto evaluate the erosion problem and monitor its future trends. Areas that are now covered by the studyinclude, erosion inventory, monitoring and study of coastal sediment budgets. In the last two years due to thecurrent threat on the immense coastal infrastructure, emphasis was also placed on producing data forplanning and erosion mitigation. The project was therefore expanded to include studies on the susceptibilityof different coastal areas to coastal erosion. Two more sub-projects are also proposed to deal strictly withcoastal hydrodynamics and socio/economic impacts of coastal erosion. These studies should produce datathat can be used for coastal development planning and management of the coastal erosion problem. On thebasis of the acquired data and information from environmental geology, the susceptibility of the differentcoastal environmental geotypes to erosion will be computed. This will establish the extent of vulnerable areasin the different risk area categories.

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 12The amount of investment threatened by erosion is of significant economic importance consideringthe fact that tourism is the leading industry in Kenya and coastal tourism is an important component.Thereis an urgent need to formulate a specific coastal zone development policy that will take into account thepeculiar problems associated with land ocean interactions.This policy must take into account the continuedviable use of the extensive coastal infrastructure and at the same time regulate development of futureinvestment.One of the problems that will face policy formulation is lack of reliable data sets. To overcome this,a more pragmatic approach must be adopted. This should utilize established civil engineering procedures,where case studies, preliminary field surveys, experience in working in an area and the limited data availableplay an important role in the preliminary project design. It is our opinion that such an approach could formbasis for the initial policy guidelines. This approach is made necessary because intending developers andpeople experiencing erosion problems today cannot wait until reliable monitoring data is collected.10. LAND USE PLANNING AND RELATED LEGISLATIONLand ownership along the coastal zone has experienced a lot of legislative changes since the first realland ownership system was established under Islamic law. The first major changes occurred in 1908 whenland titles act was introduced. This formed the first legal framework for adjudication of claims. In 1963, theregistered land act was introduced to replace all other acts. This was also associated with drawing of suitablemaps.In 1967 and 1968 two other acts, the land control and the land planning acts were introduced. Theformer to control ownership and subdivision, and the latter to control planning development. The combinedeffect of the two acts was control over transactions and land use to avoid fragmentation and speculation.Fragmentation through inheritance remained uncontrolled, even though such subdivisions could not beregistered, the act had no control over their use resulting in many unplanned developments.Other instruments that control land use include, the local authority by-laws (local governmentadoptive by-laws). These control plot sizes and all aspects of development in none agricultural land.10.1 LAND POLICYLand policy in Kenya governs the rights and obligations of land owners towards the achievement ofthe public interest with the aim of achieving optimal land use. The Kenya constitution guarantees the rightand security of tenure subject to laws and regulations governing land usage. Land issues revolve round thespecifics of land tenure systems, consolidation, adjudication and registration.10.2 CATEGORIES OF LANDThree categories of land are recognized in Kenya, Government land which includes all land ownedby the government, Trust land which include all land held in trust by the county councils and lastly privateland, owned by individuals under leasehold or freehold. Other land interests include permanent reservationsincase of government departments or minor interest in case of temporary reservations.10.3 USE AND DEVELOPMENT OF LANDThere are procedures to be followed before land is developed for the different tenure systems.Approvals must in any case be given by the relevant authorities depending on the intended project. Interestedbodies include, the commissioner of lands, Director of physical planning, local authorities and land controlboards of the central authority. Until all applications are determined, the use or development of the landshould not be carried out.10.4 RELEVANCE OF THE CURRENT LAND USE POLICY ON COASTAL EROSIONThe legislation governing land use along the coastal zone, including procedures to be followed beforeany development is initiated preceded awareness on coastal erosion. As a result, plot boundaries on theseaside are therefore put at the highest water mark, with no direct safeguards against coastal erosion.

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 13Adaptive local authority by-laws can be modified to control development and limit the structures that can beset up in different areas. The leasehold and freehold tenure system would be quite restrictive in developmentof comprehensive coastal erosion management plans due to interference directly with private land interests.10.5 EXPLOITATION OF MARINE SANDThe building policy restrict use of marine sand due to the chloride content. As a result of this andthe abundant availability of land based sand sources, permits restrict use of marine sand sources.10.6 EXPLOITATION OF REEF ROCKThe new fisheries and wild life acts prohibits trade in shells and corals, and use of destructive fishingmethods. Use of reef rock for building is therefore out of question. Building rock along the coast is obtainedfrom coral limestones of pleistocene age, that are found along the Palaeo Marine environments.11. PROBLEM RELATED TO LAND USE PLANNING AND COASTAL EROSIONKenya has an established legal framework and flexible local authority by-laws to govern landtransactions and development. However, the relevant acts have not achieved all the desired objectives dueto various limitations. For example, the legal framework does not take into account problems related tocoastal erosion especially those related to development of vulnerable environments. Another aspect that isnot regulated is construction of coastal defense structures which are considered under minor improvementworks. Even though local authority by-laws and the Registered land act limit subdivision to a certain criterionit has no control over divided use of the land. This aspect alone increases pressure on coastal zoneenvironments beyond the planned levels and has been responsible for the mushrooming of unplannedstructures.12. MANGROVE MANAGEMENT POLICYMangroves were first gazetted as forests in 1932. Covered in this gazettment was all that land lyingbetween the high and low water marks, and covering approximately 111,386 hectares. This was followed bya 1964 legal notice which declared mangroves as central forests and vested their interest in the ForestDepartment which is now responsible for their management, exploitation and use of mangrove environmentsfor any activities. The Forest Department controls exploitation of mangroves through licensing procedures.Selective cutting of specified products in designated areas based on information from the 1967 and the1981/83 mangrove forest inventory forms the basic control on utilization of the trees. However, illegalcutting and allocation of mangrove land to private developers are major problems. Other problems includelack of management plans to give guidelines on management objectives strategies and monitoring systems.As a result, decisions have been based strictly on intuitive, judgement and individual initiative of the fieldofficers. This has resulted in lack of consistency and longterm sustainability of the management decisionsand their objectives. A new approach bringing together all the interested parties culminating in a nationalworkshop on mangrove management was organized in 1993. The proceedings of this workshop will forma new basis for mangrove management.13. COASTAL ZONE PLANNING DEVELOPMENT AND MANAGEMENT POLICYKenya being aware of the need to develop sound coastal development strategies has set up, throughvarious ministries, several organizations that deal directly with coastal resources. The Kenya Marine andFisheries Research institute (KMFRI) carries out research on most marine aspects. The Coast DevelopmentAuthority (CDA) places emphasis on General Coastal Zone Development and Management <strong>Planning</strong> and theKenya Wildlife Service (KWS) is in charge of development and management of protected areas. Otherimportant departments in coastal development include the Fisheries and Forest Departments which deal withfisheries and forest development respectively. Together, these organizations form the basic organizations incharge of coastal zone resources.14. DISCUSSION

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 14Coastal erosion is widespread and has a long history pre-dating most of the modern infrastructurethat are located along the shorelines. These new infrastructure especially those erected on drift-geology areexperiencing serious coastal erosion problems, necessitating extensive coastal protection works.Available information shows that there is a strong relationship between the coastal type andpredominance of coastal erosion. The most affected areas include geological environments that aredominated by unconsolidated sediments overlying the 0 - 7 m OD terraces. Other geological environments,for example sites for the old coastal towns, Malindi and Mombasa have been relatively safe due to good siteselection.The longterm socio-economic impacts of coastal erosion could have been greatly reduced for thealready developed areas by careful planning and site selection. In most of the areas, this could have beenachieved by siting the permanent infrastructure from 50 - 200 m inland.Due to the poor site selection for the case of most of the hotels, extensive coastal protection measurescomprising mainly of vertical sea walls have become a necessity. These have been erected in most of theareas to stop shoreline retreat. However, the sea walls have induced secondary environmental problemsespecially beach erosion, resulting in rapid degradation of the beach resource, especially in Diani, Bamburiand Kikambala. While coastal protection is known to induce considerable environmental problems,considering the level of investment along Kenya's Coastal Zone, and the importance of this to the tourismindustry and the national economy, a coastal erosion protection strategy must be initiated to cover thedeveloped vulnerable areas, not only to stop shoreline retreat, but also to conserve the beaches. Carefulplanning must also be considered in the rest of the areas.Other shoreline-erosion-inducing activities include the way coastal inhabitants harvest both livingand non-living coastal resources. Of much importance are the living resources, especially the mangroves.To most coastal inhabitants, exploitation of the resources is inevitable due to lack of affordable alternativesfor example construction materials and fuel. In light of this, strategies on curbing coastal erosion problemsshould include provision of alternative resources rather than those that increase the instability of the coastline.Research on anthropogenic impacts should investigate exploitation patterns of one resource (e.g Mangroveresource), in relation to increasing exploitation of another resource of relatively less importance to coastlinechange such as marine fisheries.To achieve all the desired objectives of sustainable coastal zone development, there is also a needto review and strengthen the existing legislation and licensing procedures to incorporate policies that take intoaccount coastal erosion related impacts. There is also a need to strengthen coastal erosion research to gatherthe relevant management data.ANNEX IREFERENCESAKOU; ANN; DEIGAURD; ROLF; FREDSOE; JORGEN; AND HEDEGAARD, I.B. (1991).Application of Mathematical Models for Coastal Sediment Transport and Coastline development. I n`Third International Conference on Coastal and Port Engineering in Developing Countries.' Mombasa,Kenya.BRUUN, P. (1983). Review of conditions for uses of the Brunn rule of erosion. The Dock and HarborAuthority 64 (753). Pp. 79-82 (cited in Gibb, 1987).CASWELL, P.V. (1956). Geology of the Kilifi-Mazeras area. Report No. 34. Rep. Geol. Surv. Kenya.CASWELL, P.V. (1953). The geology of the Mombasa-Kwale area. Geol. Surv. Kenya. Report No.24.FORESTRY DEPARTMENT AND KENYA WILDLIFE SERVICES (1993). National <strong>Workshop</strong> forImproved Management and conservation of the Kenyan Mangroves. Diani, South Coast, Kenya.18th-23rd July, 1993.GHAIDAN, U. (1976) Edit. Republic of Kenya, Lamu. A study in Conservation. East African LiteratureBureau. Nairobi, Kenya. Pp. 109-112.GOVERNMENT OF KENYA. 6th National Development Plan, 1989-1993. 262Pp.GOVERNMENT OF KENYA. Maritime zones act, Laws of Kenya. Chapter 371.GOVERNMENT OF KENYA (1976). Tana River Development Authority. Upper reservoir preconstructionenvironment study.GOVERNMENT OF KENYA (1979). National Water Master Plan.GOVERNMENT OF KENYA (1981). Tana River Development Authority and Athi River pre-investmentstudy.

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 15GOVERNMENT OF KENYA (1991). Handbook on land use, planning administration and developmentprocedures. Ministry of Lands and Housing. 65Pp.HORTON, M.C. (1984). The early settlements of the Northern Swahili Coast. PhD. thesis Departmentof Anthropology University of Cambridge.IBE, A.C; QUELENNEC, R.E. (1989). Methodology for Assessment and Control of Coastal Erosionin West and Central Africa. <strong>UNEP</strong> Regional Seas Reports and Studies No. 107.<strong>IOC</strong>-<strong>SAREC</strong>-KMFRI Regional <strong>Workshop</strong> on Causes and Consequences of Sea-Level changes on theWestern Indian Ocean coasts and Islands. Mombasa, Kenya, 24th -28th June, 1991. <strong>IOC</strong><strong>Workshop</strong> Report No. 77.KAIRU K.K. (1989). Preliminary Report on Coastal Erosion in Malindi area Kenya Occasional ReportNo.2. Kenya Marine and Fisheries Research Institute.KAIRU K.K. and MUNYAO T. (1993). Environmental impact of coastal erosion in Kenya "Mitigationoptions". Presented at the <strong>UNEP</strong>-COMISSAO NACIONAL DO MEIO AMBIENTE ~<strong>Workshop</strong>on Coastal Erosion Techniques, East African Region. December 1st-3rd, 1993 Namaacha, Maputo.KENYA MUSEUM SOCIETY (1992). Kenya past and present issue 24. 52Pp.MUNYAO T.M. (1992). Sedimentology of Shirazi-Funzi Lagoon, Coast Province Kenya. M. Phil thesis,Moi University, Kenya. Pp 150-152.OJANY, F.F. (1981). The geomorphology of the coastal areas of Kenya. Eastern African <strong>Workshop</strong> onResource Policy and Management in Coastal zones Mombasa, 1981.OKEMWA, E. (1992). The Implications of Climate Change and Sea Level Rise in the East African CoastalRegion. A study of Kenya, International Convention on Rational use of Coastal zone BORDOMER92.PILARSZYK, K.W. (1991). Structural aspects and design procedure for sloping seawalls. In `ThirdInternational Conference on Coastal and Port Engineering in Developing countries'. Mombasa,Kenya. Pp. 74-88.SIMIYU SIAMBI W.M.N. (1978). Geology of the Mazeras - Mariakani area. Investigation Note: Minesand Geological Dept. Unpubl.STICKLAND, I.W.; ROWE, H.J.D. and THOMAS, R.S. (1991). A systematic approach to coastalmanagement as applied to coasts in developed developing countries. In `Third International Conference onCoastal and Port Engineering in developing and developed countries. Mombasa, Kenya. Pp 152-166.THOMPSON, A.O. The geology of the Malindi area. Geol. Surv. Kenya Report No.36.WILLIAMS, L.A.J. (1962). The geology of the Hadu-Fundisa area, north of Malindi. Geol. Surv. KenyaReport No.52

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 16ANNEX IILISTS OF SCIENTISTS INVOLVED IN COASTAL EROSION STUDIES IN KENYA(A)Actively Involved:Kairu, K.K.,Munyao, T.M. andAbuodha, P.O. (Mrs)all ofKenya Marine and Fisheries Research Institute,P. O Box 81651,MOMBASA, Kenya.Tel: (254 11) 475570Fax: (254 11) 472215Abuodha, J.O.Z.,School of Environmental Studies,Moi University,P. O. Box 3900,ELDORET, Kenya.Tel: (254 321) 43001/8(B)Associated with Coastal Erosion ResearchProf. M.P. Tole,School of Environmental Studies,Moi University,P. O. Box 3900,ELDORET, Kenya.Tel: (254 321) 43001/8(254 321) 43061Dr. Odada E. O.,Department of Geology,University of Nairobi,P. O. BoxNAIROBI, Kenya.Tel: (254 02) 449 233

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 17III.COASTAL EROSION IN KENYA : A CASE STUDY OF TH EMOMBASA DIANI AREAby Mrs. Pamela Atieno AbuodhaABSTRACTThe overall objective of this paper is to identify coastal zone management problems within Mombasa Dianiarea. Other objectives included evaluating the effectiveness of the existing control measures and identifyingresponse strategies for the affected areas. The results showed that coastal dunes and beach ridges, cliffedcoasts and backshore areas could be developed but with proper set back lines so as not to induce erosion.Coastal zone management system, and construction of stabilizing structures along the beaches were identifiedas major problems within the project area. From these result it is concluded that there is an urgent need fora coastal zone management system and to enact a legislation which would protect coastal resources andenvironment for their sustainability. Stabilizing structures should be constructed only for highly developedareas. Keeping in mind the future sea level rise, beach hotels should be put about 1 km. landward of theshoreline.1. INTRODUCTION1.1 STUDY OBJECTIVESThe study objectives of this paper are as follows:(i)(ii).Identify major morphological features within the study area in order to determine the vulnerabilityof the coastline to sea level rise and impacts of coastal development.Assess the vulnerability, response strategy and requirements for the affected areas.1.2 STUDY AREAThe study area is situated on the southern section of the Kenya coast (Fig.1). It stretches over 70km.between latitudes 3 53' south and 4 26' south. The physiography of the study area include islands bays,estuaries, reefs and beaches (Fig.2). The coastline north and south of Mombasa are characterized by coralreefs and sandy beaches protected from the open Indian Ocean by the fringing reefs.1.3 GEOLOGICAL SETTINGThe coastal belt of Kenya comprises of the following main topographical features which are closelyrelated to the geological characteristics of the area. These are the Coastal Plain, the Foot Plateau, the CoastalRange and the Nyika. Geological features within the Coastal Plain comprises of Reef Limestones, Kilindiniand Magarini Sands. (6 Fig. 3). The Reef Limestones provides the carbonate sands after weathering.2. RESULTS ON MORPHOLOGY2.1 MAJOR MORPHOLOGICAL FEATURESCLIFFED COASTSCliffed coasts were observed at Kanamai, Shanzu, Iwetine, Nyali, Likoni [Fig.4) and at Black CliffPoint as well as Tiwi (Fig.5). The height of these cliffs ( Plate 1) was estimated to be 10 -15 m above sealevel. (Abuodha, 1992). The cliffs are near vertical with pronounced wave cut notches at 4 m above sea level(Ase, 1978). Where the forces produced by the action of waves and the compression of trapped air puncturethe roof of an overhanging cliff, water and spray are driven up through blow outs observed at Kanamai(Plate 2).

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<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 23COASTAL DUNESCoastal dunes were observed at Shanzu, Bamburi and Nyali (Fig.4). The dunes are located close tothe shoreline thus they form a bufffer stock of sediments that can be reshaped by the swell and can influencethe equilibrium of adjacent beaches.SANDY BEACHES AND ROCKY SHORESExtended beaches occur north of Mtwapa Creek at Kikambala and Kanamai, and north of TudorCreek at Bamburi-Kenyatta and Nyali (Fig.4). They also occur at Tiwi and Diani (Fig.5). Rocky shoresoccur at Shanzu (Plate 3), Kenyatta, Iwetine (Plate 4) and Galu.SHORE PLATFORM AND LAGOONSThe shore platforms are evidently developed and widened as the cliffs recede, and shaped by theaction of waves and other marine processes. Evidence of wave abrasion can be observed on shore platformwhere the more resistant elements of rock persist as stocks and intervening areas have been scoured out aspools (Plate -1; 4) lagoons are located within the shore platform and between the beaches and cliffs, and alsowithin the raised shore platform. The lagoons are 5 -10 m deep and 400 - 800 m wide.3. COASTAL ZONE MANAGEMENTCoastal problems in the study area were identified to be:(i)(ii)(iii)Lack of coastal zone management systemCoastal erosion; anddegradation of beaches.Human interferences are having major impacts on the coastal zone and therefore there is increasingacceptance of the need to protect the marine environment and its resources. Coastal erosion is a prevalentphenomenon along the Mombasa - Diani area. In many places, the rate of coastline retreat and the resultingenvironmental degradation and economic loss is on such a scale as to be alarming (Plate 5, and 6).Beach degradation was found to be as a result of 5 major activities namely:(i)(ii)(iii)(iv)(v)constructions beyond high tide marksweeping of the beaches,aesthetic activities on the beachesbeach mining; anddischarge of waste waters onto the beaches.The sand used for constructing sand-infilling structures is obtained from the adjacent beaches or thedunes along the shore. Erosion is thus accelerated due to no exchange of sand between dunes and the beach.Seaweeds are swept and buried on the beach. The loosened sand is easily eroded into the lagoons or onto theshore platforms during flood time. Playing games such as volley ball foot ball and the building of castles alsoenhances beach erosion. Limestone is mined on the shore platform to make traditional grinding stones andsand is removed from the beaches to be used in the ash-trays.The beach hotels dispose of their wastes especially from the swimming pools directly into the sea.These wastes erods volumes of sand which affects marine life such as coral reefs. The health of swimmersis also affected not to mention the children who play in these waters.4. COASTAL PROTECTION MEASURESThese includes the construction of seawalls, revetments and groynes. Beach nourishment andplanting of grass is also practiced along Nyali Beach. The protection using seawalls has failed as can be seenin plates 7 and 8 seawalls are the major forms of protection in the study area. Building such

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<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 28structures causes very drastic changes on the beach which include the increase of intensity of longshorecurrents, hastening removal of the beach. They also concentrate wave and current energy at the ends of thewall, increasing erosion at these points.5. RECOMMENDATIONS(i)(ii)(iii)(iv)(v)(vi)(vii)(viii)(ix)(x)(xi)(xii)Shoreline areas undergoing erosion may be developed with proper care taken by creating a bufferzone.Stable area need careful development plans so as not to initiate erosion.Depositional areas are best for development if consideration is taken not to create erosion.Beaches occur within transitional areas and any constructions placed adjacent to them should bewith appropriate set back line.Constructions are however encouraged on raised areas such as the coastal cliffs, stable coastal dunesand beach ridges.Structures constructed near the shoreline should be considered by law to be temporary thus shouldnot be protected in any artificial way and should be let to fall when their time come.There are 3 basic options in response to the erosion problem.- no action- relocation of endangered structures- positive corrective measuresNo action should be taken particularly if no houses are threatened and only undeveloped land or inexpensive structure are in danger. In other words, erosion becomes a problem when economic lossesare imminent. Kanamasi, Kenyatta, Nyali and Leven are examples.Structure at Kikambala should be relocated. The required set back must be carefully evaluated, inorder to avoid further relocation of the same structure in the near future.Positive corrective measures should only be taken for a highly developed beach such as Bamburi,and a regional breakwater should be used rather than seawallsWhichever option(s) is chosen between the three, the present and future sea level rises should betaken into account.Lack of coastal management system was found to be the major coastal problem within the studyarea. There is a urgent need to have legislative capability to safeguard the optimal use of coastalzone resources. There is also need to have a long term program on the environment and it resources.ANNEXREFERENCESABUODHA, P.A. W., 1992. Geomorphology and Sedimentology of the Mombasa - Diani area;Implication to Coastal Zone Management. M. Sc. Thesis. Univ. Nairobi 158p.ASE, L.E., 1978. Preliminary report on studies of shore displacement of the southern coast of Kenya.Geogr. Ann. Ser., A60 (3-4)- 209 - 221

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 29IV.STATUS OF COASTLINE CHANGES IN MAURITIUSby Dr. L Joottun in collaboration with D. Gangapersad, S. Ragoonaden, K. Dunputh, I. Ujodha1. PHYSICAL ENVIRONMENT1.1 GEOGRAPHICAL SETTINGMauritius is a volcanic island located at latitude 20's and longitude 58 East, in the Indian Ocean,some 800 km from South East of Madagascar (Fig. 1). It has a land area of about 1860 km² with a maximumextension of 60 km from North to South and 50 km from East to West. It has a mountaneous topography withthe highest peak reaching 817 m and about 50 rivers and rivulets drain into the lagoon. The coastline is about200 km long and is almost completely surrounded by a fringing coral reeef system, enclosing a lagoonal areatotalling 243 km². With no continental shelf as such the water depth reaches 3000 m within 20 km of thecoastline. Some major islands that dot the Mauritian sea are Rodrigues, St Brandon, Agalega and DiegoGarcia. These islands are inhabited. There are also other and smaller islets around the mainland that stillhave their pristine characteristics.1.2 THE COASTAL ZONECoral reef systemThe coastal zone of Mauritius is surrounded by coral reefs of fringing type, except at few places andnear river mouths. Off the southern coast a stretch of 15.5 km and off the west coast for 10 km this reefsystem is absent and waves break directly on the coastline. The total length of this reef is about 230 km, witha lagoonal area of 243 km² (Fig. 2).The reef system comprises:(a)(b)(c)(d)a sedimentory zone made up of an accumulation of sand, coral rubbles and basaltic and beach rockfragments and also some sea grass and algae.A reef flat at some places with coral growth but generally devoid of fine sediments. Presence ofmarine algae are predominant in many areas. Waves breaking on the reef front dissipate their energyat this junction.A reef front which is usually indurated and lithified coral substrate. It is generally shallow withinsignificant amount of coral rubbles. This unit is generally under strong hydrodynamic conditionsdue to breaking of waves.Outer SlopeThe outer or frontal part of the reef is composed of alternating ridges and grooves carved out bywave action armed with rock fragments. The bottom of the grooves is covered with sand and coralrubbles. On the spurs porites, pocillopora, faviidae and millepora sp. etc are noted.Coral reefs areamong the most biologically productive, taxonomically diverse, aesthetically beautiful communityof the coastal zone. While their massive structure provides a buttress against wave assault, theirbiological productivity yields a good source of protein to man. Besides, they offer many attractionto skin and scuba divers. They also produce the major percentage of calcareous sands. In manyregions of Mauritius and Rodrigues human activities are inducing serious harm to the coral health.Discharge of industrial effluents, run off contaminated with silt saturated with nutrients, sewerwastes, activities such as dredging of coral sands, poling, anchoring and walking over the coralstructures are gradually killing the coral population. The situation has become so dramatic that incertain regions of the island the percentage of coral population declined from 60% to 20%. It is inthis connection that the Government of Mauritius is creating two marine parks; one on the westerncoast and the other in this south eastern one, with a view to improving the coral health and maintaintheir diversity, so that the present and future generations could benefit from them.

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<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 32(e)PassesThese correspond to major topograhic depression which interrupt the reef formation along all itswidth, to the level of the back reef depression of variable length and width (15 m to 2,500 m) theyhave depth of mean value 20 m, exceptionally to 50 m (South and North entrances Mahebourg). Thistype of discontinuity is generally directly related to the hydrodynamic network, or in relation to thepresence of springs or resurgences (Trou d'Eau Douce).The internal slope of the passes are characterised by a complete morphological difference in viewof their orientation in relation to major predominant currents and localised regimes of sedimentdynamics.In sheltered zones following sandy accumulations of the back reef, a narrow sandy platform developsdown to 5 m approximately, characterised by the presence of necrosed coral patches, recolonised bypheophycea and sparse populations of Halophila sp. The joining towards the beds of passes iseffected through the intermediary of sedimentary thallus of high declination (15 -45 ), interceptedby sub-horizontal "ressauts". Under high sedimentation, these sectors offer possibilities of only lowdensity live forms.In unsheltered zones, are differentiated either a zone of organised spurs and grooves (South andNorth Entrances Mauritius) or an eroded bioconefructed thallus and highly declined (45 -60 ),characterised by a succession of narrow steps of 1 to 2 m in declining levels with locally encounteredpatches of algal nodules (Passe Sud-Est, Rodrigues) Around 5 metres, these are replaced by decline(75 -80 ), totally colonised by madrapora sp. As from 10-20 m, appears a sedimentary thallus of15 -30 inclination, fed by the debris of organisms living in the superior horizon, and partly jointedby a muddy-sandy fraction. Where they subsist, bioconstruction are represented by Madrepora sp.Near the 20-25 m isobaths, the detritic thallus joins abruptly with a muddy-sandy bottom slightlymoulded with tumulus and funnels of enteroprenetes, or with a bottom made up of rough sediments,(gravel type). (Port Sud-Est, Rodrigues).The lagoonsThe lagoon is the area between the fringing reefs and the shoreline. This distance varies between fewhundred metres to six kilometres. In the west from Flic en Flac to Baie de la Petite Riviere and from southof Pointe aux Caves to Pointe aux Sables and in the south from Roche qui Pleure to Pointe Naturel thefringing reef is significantly absent. In general the lagoonal depth is comparatively shallow (1-2m) with theexception of Mahebourg where water depth reaches 15 m in the inner reef pass. Significant depth have alsobeen recorded in the area of Ile d'Ambre, Riviere de Rempart, Riviere Noire and Blue Bay. The bottom ofthe lagoon harbours various plant and animal communities, coral colonies, coral rubbles, assemblages of coralsediments and terrigenous materials near the estuaries, tidal flats, mangrove fields and juxtaposing uplandsuch as in the south west segment. At quite a few places such as Pointe d'Esny, Pointe des Regates, DeuxFreres, GRSE, Roches Noires, Pointe Lascar, Poudre d'Or, sand is being mined from the lagoon with spadeand bucket and transported to the shore in boats. Many fishermen gain their livelihood through catching fish,shrimps, octopus, lobster, oyster in the lagoon. With the discharge of industrial effluents in the lagoon, thesemarine faunas are gradually decreasing. Oceanic swells crashing against the reef form a surf area in thelagoon and the sea water move up the beach or along the beach to be drained off through the passes. Sedimentare thus transported along the beach through drift or across the beach line to the deep sea through various reefgaps. The lagoonal area affords much recreational activities such as boating, skiing, surfing, pedaloing,snorkelling, scuba diving, para sailing, etc, to local as well as to tourists.The ShorelineThe shoreline of Mauritius is extremely variable in terms of size and nature of deposits, extent, slopeand energy regime. The width of the beach varies location wise from few metres in the Eastern and Southernregions to about 25 m in the north Eastern and eastern ones. The sediments are coralline in nature except inthe south western segment, near barachois and major river confluence, where they are muddy with largefractions of silt and clay. The coastal areas which are in proximity with the reef such as in the eastern andsouthern section, the sand deposits on the beach and backshore are very coarse, rounded and spherical.Abrasion of the coral fragments and their attrition during transportation have imparted such grain structuressignificant of high energy regime.

The shoreline has been zoned laterally into the following:<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 33ForeshoreIt comprises the intertidal areas and includes the lower and upper foreshore. It extends from a fewmetres to 60 or more metres. The upper foreshore is narrow and steeper (10-20%) with medium tocoarse sands where as the lower foreshore is gentle (6-10%), with fine sands to pebbles, cobbles andboulders. This feature is well developed in the north eastern, north western and eastern regions,however where rocky platforms is exposed it is insignificant. Its slope and granulometry, energyregime and physical protection are the determining factors of beach stability. Besides the reefs, thisis the first and foremore zone that bears the brunt of wave assault and protect the backshore and thedunes.BackshoreIt is a nearhorizontal feature comprising very coarse grainsize, with a convex surface and usuallysloping landwards. The berm is a typical feature of this zone and has a steep front from where thereis a change in grain size. Its width varies between 3 and 12 m. The proximal seaward slope rangesfrom 20-25% while the distal one varies between 5 and 10%. It represents a unique energy regimewhich is attacked by plunging breakers and eolian agencies. Sediments are characteristicallyrounded, platy, subspherical or cylindrical. Where ridge erosion is prominent the upper layer of thisdeposit is finer. Contamination of finer sediments from the dunes is not uncommon. The functionof this deposit is attributed to strong energetic waves. During spring tides or stormy weatherplunging breakers attack the berm, scouring and churing the sediments and swirling them down thebeach to be rebuilt by constructive waves during conducive environment.Dunal ridgeDune and ridge complex are characteristic features that lie above the berm line. They are linear,undulating, hummocky and run paralell to the coastline. The ridge complex comprises sediments ofdifferent size and grade but is generally coarser. The clastic particles are subrounded and poorlysorted. The sand dune sediments are fine grained, subrounded and well sorted. Their windward faceangle is comparatively gently 11-12% while the slip face angles varies between 15-20% or more.The dunal deposit has been aggressively mined and the mining vestiges could be observed atRiambel, St Felix, Pte d'Esny, Riviere des Galets, Poste La Fayette, Flic en Flacq, La Cambuise, BelOmbre. The coastal area at and near the sand quarries have been seriously degraded. Anydevelopment in connection with residences or hotel complexes would give rise to seriousconsequences. As the dunal ridge acts as sand reserve and compensate for any loss due to naturalforces, the beach in these areas are getting highly eroded. e.g Pomponette, Bel Ombre and inRodrigues, Bar Brule and Anse Ali.At Flic en Flac the mining of the dunal deposit has created a depression of more than 2 m and thissite has been backfilled and parcelled out. With the rising sea level, as this parcelled area is stillbelow the coastal road, there is a very high risk that this site would be overflooded, thus giving riseto unimaginable environmental problems. The quarried area at Pomponette would be most affectedas it is behind the coastal road and 2-3 m below it, that is below amsl.The only undegraded huge dunal deposit left is at Le Souffleur. This deposit is about 1 km long, 12m high and about 100 m wide. The feature is presently supporting grasses and filao trees and partof which is used for grazing. The Government of Mauritius is keen to protect this last vestige anda last attempt to exploit this massive deposit has been warded off. Similarly every attempt is beingmade to save the few remnant dunal deposits in Rodrigues.BackswampBehind the ridge lies lowlying flat ground called backswamp, tidal flats or tidal marsh. Thesediments are silty and clayey and during high tide or rough sea this area is overflooded. It supportan important array of coastal flora and faunas.Mangrove SwampsIn some segment of the coastal region such as near river mouths or estuaries e.g Terre Rouge,Riviere Noire, Baie du Cap, Riviere du Rempart or where there is a resurgence of fresh water nearthe sea. Such as Trou d'Eau Douce, Poste La Fayette, Bras D'Eau, Roches Noires, Poudre d'Or, a

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 34colony of salt tolerant intertidal tree species form a flat muddy ground or swamp. These mangrovetrees are of direct economic and ecological importance and some of their functions are:(1) Protection of the shoreline from erosion due to cyclonic weather conditions and stormwaves. They also exert a breakwater effect in absorbing most of the energy of storm drivenwave action, thus helping to protect housing and service structures further inland.(2) Mangrove ecosystem is a major nursery ground for many economically important marineorganisms including some plant communities.(3) They also fuel food generating activities from their parts that go into the good chains andthat support fisheries production.(4) They also harbour a host of waddling and fishing birds.They entrap terrigenous sediments that would otherwise get deposited on coral population withconsequential effect on the production capacity of the marine ecosystem at that locality.Although tolerant to high salinity condtions mangroves reach their best development in polyhaline(estuarine) conditions. Very often competition for space and nutrients limit the landward extentionof mangrove swamps while salt stress may suppress maximum productivity under fully marine orhypersaline conditions. Modification of estuarine salinity patterns by upland drainage and othersubsurface control structures have profound effects on mangrove community and its associatedfisheries.The present state of mangrove health in Mauritius and Rodrigues is poor. Lots of damages havebeen done to this plant community due to irrational coastal development. With the construction ofmany hotels on the coastline mangrove stands have been vanished and the remnants are in a very badshape. The Ministry of Agriculture, Fisheries and Natural Resources has undertaken serious andconcrete step to rehabilitate this important plant community. Tens of hectares of the coastal area hasbeen planted with new stands in Mauritius and in Rodrigues and a new COI project will soon beimplemented in Rodrigues for further stabilising the coastline with mangrove plantation.Coastal WetlandCoastal wetlands are ecologically sensitive areas and play a vital role in the functioning of coastalecosystem and the maintenance of high level of sustainable carrying capacity. They provide the essentialhabitat for many important marine species such as shore birds, crabs, fish, shrimps, worms etc.Wetland vegetation plays a keyrole in converting organic compounds(nutrients) and sunlight into thestored energy of plant-tissue. The dead leaves, branches and stems of trees are broken down in the water bybacteria and consequently, leave the storage energy and become available organic detailed food for thevarious organisms inhabiting there. A fraction of these nutrients are partially recycled within this system butthe major portion often find its way into the coastal waters to provide basis nutrients for the food chain of thecoastal water ecosystem.Some of their other major functions are:-1) wetland vegetation remove toxic materials and excessive nutrients from coastal waters. Siltysediments and other inert suspended materials are physically removed from the water and depositedin the marsh thus sparing the coastal water from heavy sediment load that causes incidence ofentrophication and sedimentation of tidal inlets,2) They also slow surges of flood water and hence act as flood regulator,3) They also play an important role in absorbing and retaining dissolved chemical nutrients such asphosphates, nitrates, nitrites, ammonia etc,4) The shape, vegetation and fauna impart a particular beauty which is unique in the coastal zone.In Mauritius, particularly in the Northern and North Western region many coastal wetlands haveeither been completely filled up or partly reclaimed for major coastal development projects such hotel andbungalow constructions. The incidence of flooding of residences and hotels in Grand Baie and Pereybereregions (Fig. 6) is due to the construction or suppression of these wetlands and the obliteration of the tidalinlets and natural drains. During heavy rainfall many houses and shops lying at or near the wetland are

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 35flooded and the inhabitants have to vacate their residences. Disposal of sewage becomes a serious problems.With the filling in of Mare Michaux and Grande Mare Longue, and the resiting of Road B 13, behindMauricia Hotel, part of Camp Carol is, during heavy rainfall flooded. This problem has been compoundedwith the obstruction of five natural drains that serviced these wetlands.The incidence of eutrophication in the northern and north wastern sea has also been attributed, to amajor extent, to the suppression of drains and change in the drainage pattern of the marshes that are notfunctioning to their optimum ecological capacity.1.3 ENVIRONMENTAL PARAMETERSLocated in a central position in the Indian Ocean at Latitude 20'S, and Longitude 57 20'E, Mauritiusis under the influence of the South East trade winds, through most part of the year. These trade winds providethe most substantial wave action that dominate the depositional dynamics particularly at the Eastern andSouthern Coastline. The tropical cyclones and anti cyclones also incluence the coastal configuration anddepositional pattern of the coast.Sea Surface TemperatureThe sea surface temperature obtained from weather stations on ships, in the vicinity of Mauritius isfound to be lowest (23.3 C) in September and highest (27.9 c) in March, with an annual mean of 25.7 c,from 1971-1980.TidesTides are diurnal to semidiurnal, with two lowtides and two high tides daily. Tidal range variesbetween about 0.5m at neap tides and 0.6m at spring tides. This negligible variation reflects the absence ofthe influence of adjacent landform features such as converging coastlines, which would favour tidaldevelopment.Water LevelsThe decrease of the barometric pressure during the passage of cyclone has considerable effects onthe rise of the sea level and such phenomenon causes dramatic effects on the coastal stability. Followingcyclone Carol in 1960, Mc Intyre and Walker (1964) estimated the level of the smarsh zone above mean sealevel at numerous locations around Mauritius. As per their estimates the elevators were mainly between therange of 2 to 3m, however, at some localities level approaching 4m were noted (Fig. 7). The presence orabsence of the fringing reef, its configuration and distance from the shore line, form and relief of thecoastline, slope and roughness of the beach face, interact together with wave and wind regime to cause theelevated sea levels.Montaggioni (1979) suggested that Mauritian coastline has experienced episodic sea level fluctuation.The sea level was -3.5m with respect to present levels 4500 yr.B.P. The average sea rose to attain the presentlevels between 2000 and 1000 B.P. Studies conducted by the Mauritian Meteorological Services and reportedby the National Climate Committee (1991) indicate a sea level rise of 1.2mm/yr and this rate is consistentwith the projected 65cm by 2090).WavesWave height, period and direction are the functions of location, wind speed, fetch area, and durationof the wave generating wind field. In Mauritius the following three principle types of waves affect the coastalzone:-

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<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 37Southern WavesoWeather system consisting of low pressure cells passing the South of Mauritius (around 40 South)can generate fully developed seas due to high wind speeds, large fetch areas and long durations.These waves reach Mauritius from the South West in the form of long period swells.Trade Wind WavesThe prevailing South East trade winds may produce short or long period waves depending on windspeed and duration. These waves travel in the same direction as their associated wind fields.Cyclonic WavesMost of the cyclones reach Mauritius from directions between East and North West and henceproduce cyclonic waves from such directions. These waves are well formed and they havedevastating effects on the coastline.Wave DataVisually observed wave data for passing ships (VOS) is the main source of historical wave data forthe Mauritian area, though a wave rider was installed in the Southern Coast of Mauritius (Riambel).With the VOS two types of waves are measured, swell and wind waves. It should be noted that thetotal wave height occuring at a point due to the combined influence of wind waves and swells is notequal to the sum of the heights of the wind waves and swells. The total height is a function of thewave energy which is proportional to height squared.Wave DirectionThe predominant direction for both wind waves and ENE swells is from the East (Table 2). Thedirection sector extending from ENE to SSE contains over 80% of all observed directions for bothwind waves and swell. Wind waves and swells from the NW sector occur less than 2% of the time.The influence of Southerly swells is noted by the fact that swells in the sector S to SW occur 13.6%of the time where as wind waves in the same direction occur only 5.1% of the time.Wave HeightIt can be seen from (Table 1) that height for wind waves is less than 1m while for swells the averageheight is close to 2m. A height of 3.48m is exceeded 1% of the time for wind waves while theequivalent height for swell is 5.39m. For more than 13% of the time swell heights are greater than3m.Wave PeriodicityMost of the wind wave periods are less than 8 seconds while most of the swell periods areconcentrated between 4 and 11 seconds (Table 3). The occurence of periods greater than 11 seconds(5%) for swell is significant and even longer period is expected especially from South West.CurrentsCurrents are generated principally by the action of wind, waves, tides,temperature and salinity.Current generated by wind and waves are of extreme importance for sediment movement in thecoastal zone. This phenomenon is more pronounced during cyclonic conditions when strong wind,high amplitudes waves and raised water level interact to give a very strong current regime.No systematic studies on water currents in the lagoon or outside the lagoons have beenundertaken,except for the NNW where recent current meters were hired from overseas and placedat 2 sites off lagoon.Hydrographic stations from this part of the Indian Ocean indicate a general westerly to Southwesterly directions, as part of the Southern edge of the South equatorial current, ship drifts indicatethat the flow speed should be between 0.3 and 0.5m/s.A few free drifting, satellite-tracked buoys indicate a multitude of directions. The sector betweenNNW and SSW contained about two thirds of all observations. Drift speeds varied between 0 and0.6m/S, with an average of 0.23m/S. The water current in the shallow water around the island, atsome places are more than one meter/sec.

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<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 40The Fisheries Division of the Ministry of Fisheries has recently undertaken current metering in thelagoon of Mauritius and their observations and results are at ( ).Bathymetric Chart of the exclusive economic zone of Mauritius (1988) gives the speed of watercurrents at specific sites around the islands.- Off Pointe aux Cannonniers (N): 2-3 miles (M)- Off Cap Malheureux N: 2-5N,- Off Blue Bay (SE): 1-2N,- Off Riambel: 2N,- Off Baie du Cap: 2-3N,- Off Le Morne: 4-5N in the East-West direction,- 2-3 is in the North-South direction.The two directions for water currents are due to the low and high tides.In the lagoon near the passes rip currents are predominant during the ebb tide.Longshore currents are also noted at the lower foreshore occassioned by the oblique incident waterwaves on the beach time. There is a reversal of direction in Summer and Winter Periods. This currentis responsible for the sediment drifting on the beach.1.4 TIDAL WAVESTidal waves sometimes occur around the southern coasts of Mauritius. A case study of such aphenomenon which occured in 1987 is attached in the annex.Wind ClimateLocated in the northern extent of the sub-tropical anti-cyclone area, Mauritius is under the influenceof the South East Trade Winds throughout the year except for short period when tropical depressions are nearthe island.2. EROSIONAL SITES2.1. GENERALThe coastline of Mauritius is under the process of pronounced morphological changes. There is anapparent evidence of marine transgression demarcated by:(1) Cliffy nature of the dunal ridge complex and juxtaposing against the upland.(2) Presences of rock stacks in the south eastern and southern segments.(3) Crenulated nature of the coastline.(4) Presence of newly abraded rocky platform.(5) Presence of wave carved caves at the HWM.(6) Inundation of the coastal roads by seawater.(7) Extirpation of trees on the backshore by seawater.These manifestations are observed during normal climatic conditions, thus signifying a gradual seaencroachment. The scouring of the backshore and the dunal ridge complex is ubiquitous so that a beach bluffof 1 to 2 m are invariably noted in many coastal segments, particularly in the western, southern and southeastern ones.There is no distinct morphological features and coastal processes that could ideally differentiate anddemarcate the various coastal segments into discreet characteristic sites. However, with a view to identifyingthe erosional patterns and the energy regimes, the whole coastal segments have been subdivided into five cells(Fig. 3).CELL A:Segment from Roches Noires to Cap Malheureux

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 41CELL B:CELL C:CELL D:CELL E:Segment from Cap Malheureux to Flic en FlacSegment from Flic en Flac to Le MorneSegment from Le Morne to MahebourgSegment from Mahebourg to Roches Noires.2.2. CELL A (ROCHES NOIRES TO CAP MALHEUREUX)The coastline in this section is bisected by many small creeks, tidal inlets and a major river, Rivieredu Rempart. The tidal marsh near the Bras d'Eau and the tidal flats and mangrove swamps near the riverconfluence are striking.The sediments are, depending upon the proximity of river or tidal inlets, calcareous or muddy, fineto coarse. At most of these places terrigenous sediments abound. Basaltic boulders of size varying betweentwo centimetres and 3 metres, as well as exposed bed rocks are common. The discharge of fluviatileterrigenous sediments as well as the scouring of the upland by wave action have given rise to a muddy beachwith flat topography. The cohesive nature of the sediment have imparted a good protection against waveaction, so that the beach and backshore are more or less protected.A typical cross sectional profile indicates a narrow backshore of 3-4m abutting against the upland.oThe foreshore varies between 3 and 10m and slopes seawards at an average angle of 8. The coastline isretreating and beach cliff of 60cm to 1.6m is predominant. It should be noted that at Roches Noires, PointeLascars and Poudre D'Or lagoonal sand mining are undertaken.The discharge of industrial effluents from three textile factories at Ile D'Ambre is taking heavy tollon the marine lives. Significantly, the presence of some structures such as fishlanding platforms, groynes andjetties at Cap Malheureux are sensibly affecting coastal protection and beach stability.2.3 CELL B (CAP MALHEUREUX TO FLIC EN FLAC)Because of the general orientation of this stretch of coastline, the predominant south east trade windsblows in a more or less offshore direction. Because of this orientation the northern sector is most protectedfrom incident wave energy, both trade wind generated as well as the large swells emanating from the south.This sector is however, extremely susceptible to cyclone generated waves which usually originate from northwest to north.Unlike Cell A, this cell comprises a comparatively more curvilinear coastline except at the bays andrivers mouths. Beach deposits are predominately coralline and basaltic, with sediments medium to coarseon the beach and finer ones on the dunes. Beach cliff of 1.5 - 2.0m have been noted at Les Cannoniers, GrandBaie and Flic en Flac. Cliff of 1.0m and observed at many places. Near La Mecque basaltic cliffs of 30-35mis very striking and the foreshore deposit is cobbly and bouldery, of basaltic in nature.The approximate length of the coastline is about 50cm; presence of wave carved caves near Pointeaux Sables and impingement of waves on the basaltic cliffs are typical of erosional features. A fairlyextensive coralline beach is noted at Pointe aux Cannonniers. Because of the passes in the fringing reef andthe prevailing direction of the cyclonic waves heavy beach erosion, with cliffs of 2m high are observed (Fig.4).The position of high water line at Flic en Flac have moved tremendously fast since the past 15 years.It was at a distance of 8m from its present position, one and a half decade ago. Since 1990 the coastline hasreceeded to 2m near the Flic en Flac public beach at Pearl beach hotel, as evidenced by the uprooting of filaotrees from the ridge complex and retreat of the coastal line to the foot of the seawall.The scouring of the ridge has given rise to a rectilinear coastline. The eroded materials that aredeposited on the beach are reworked by long shore current, thus modifying the beach slope. The presence ofa vertical seawall infront of Pearl beach has accelerated beach erosion at this junction, where wave reflectionhas eroded the foot of the wall as well as the section adjacent to the wall in the north.

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<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 442.4. CELL C (FLIC EN FLAC TO LE MORNE)The coastal segment from Flic en Flac to Le Morne is more or less protected by the south east tradewinds, but is affected by some swells. This area is bisected by many rivers and estuaries e.g. RiviereTamarin, Grand Riviere Noire, Petite Riviere Noire.The beach deposits are generally muddy, except in the southern area which is predominately sandy.Erosional scarps of 1.2 to 1.5m have been noted at Wolmar, Tamarin and Le Morne. The beach infront ofLe Morne Brabant Hotel is seriously affected by erosion. The beach line at one spot has retreated to at least10m since the past 15 years. At one junction a retreat of 4m have been observed during the past four years.The beach deposit has been eaten up and part of a walk way has been washed away and many filao treesuprooted. Although the majority of the southerly incident deep water wave energy is dissipated followingbreaking on the fringing reef, a portion of this energy related to the ambient water level penetrate into thelagoon. Strong wind from the south also generate northerly flowing currents.The extensive and deeper lagoonal area north of Pointe aux Pecheurs acts as a drainage channel tothe water levels built up due to wave action along the fringing reef fronting the shoreline. The erosionalproblem is compounded by the presence of some ill designed groynes that are inducing rip current effects andexacerbating the erosional problems. At this locality the current speed of up to 1m/s has been measured. Itis worth noting that the eroded sands from the southern region are deposited in the northen side. The littoraldriff is from south to north.The site near Berjaya Hotel, Le Morne to Pointe Sud Ouest is also under erosional process. Thebeach sand are coarse to very coarse and beach cliff of 1.5-1.8m are present all along. The dunal deposit hasbeen levelled down during the construction of Berjaya hotel and wave action is gradually enacting upon thenew depositional features, thus giving rise to beach bluff. The steep beach slope is not a natural declivity butis a result of beach push piling of sands. There is a very high risk that the ridge area will be overtopped byseawater during rough seas, affecting the hotel complexes and the other infrastructures.2.5. CELL D (LE MORNE TO MAHEBOURG)Unlike the other segments, this portion of the coastline is under constant attacks by high amplitudewaves, reinforced by the south east trade winds. The impacts of the wave energy on the beach front is muchpronounced. The opening of reef gap on the fringing reef have contibuted to the wearing of the beach front.Invariably all the coastal segments are heavily eroded. Beach cliff of 1.5 to 2.0 m could be observed nearRiviere des Galets, Pomponette and Riambel (Fig. 4). The erosional problem is compounded by the quarryingof the dunal deposit and also because of the levelling of dunes and construction of residential complexes onthem.The worse eroded sites are at Pomponette and Riambel. At this junction the incident waves aregradually scouring the beach front, further retreating the shoreline. During the past three years beach retreatof 4m has been measured. Steep scarp of 2.0 m is common and the coastal tracts and many filao trees aregradually falling prey of wave attacks.Beach erosion at Pointe D'Esny and Blue Bay is not so extensive because of the presence of manyvertical walls and groynes. There is a total absence of beach deposit at the foot of the walls and the groynesare ineffectively arresting sediments from one direction. Near Croix du Sud, during high tide the sea waterincurse upon the road and adjacent upland, clearly signifying coastline movement.2.6. CELL E (MAHEBOURG TO ROCHES NOIRES)This section of the coastline manifests sea level fluctuation since the pleotocene period. Rock stacks,detached basaltic rock outcrops and rocky promontories are very common. All these features are erosionalrelicts and have been carved out by wave action on the basaltic rock outcrops. This indicates that thestrandline was about one or more kilometre and have gradually retreated since the Pleistocene period.Because of the absence of good beach deposit from Mahebourg to Grande Riviere Sud Est, beacherosion manifestation is not vivid. However, on careful observation it could be remarked that the sea levelis verily encroaching upon the backshore. Rocky cliff and wave abraded platform are commonly observed.

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 45The area of Trou d'Eau Douce and Belle Mare are under the pronounced effect of coastline changes.At Trou d'Eau Douce a scarp of 1.6m and a landward shifting of the coastline by 3.5m had been observed in1991, such change in morphology is due to the climatic variation compounded by the uprush of swellsimpinging upon the coastline. On the north of this site severe beach erosion has been noted. This problem,as per information, is due to the opening of a pass in the reef that causes seawater to funnel inshore, thuseating up the coastline.Pointe de Flacq near St Geran has experienced beach erosion since 1988. Cliff of 1.8m have beenmeasured all along. The proximity of the fringing reef and a gap in the north have induced this degradation.The surging water is seen to scour the beach and ridge deposit, churning them and tranporting them alongshore. Very coarse sands, granules, cobbles, boulders are omnipresent. The presence of a beach rock has,to certain degree, protected the beach deposits. Towards Roches Noires the beach front is protected eitherby virtue of this coastal configuration, or due to the presence of rock outcrops or due to the presence ofmangrove swamps. The decrease in the mangrove stands is a serious cause of concern.From Poste la Fayette to Roches Noires, the coastline has undergone less damage, however towardsthe Roches Noires bridge the beach deposit is gradually decreasing and during low tide the bed rock isexposed. This situation is being seriously influenced by extensive lagoonal sand mining.3. FACTORS CONTRIBUTING TO SHORELINE CHANGESFluctuation of sea level rise is a manifestation brought about by many factors, though one maypredominate upon the other. Human interference have accelerated the shoreline changes through a series ofunplanned and often irrational development. History testifies that during the past, sea level fluctuationoccurred quite a number of times where a rise of more than 100 m have been identified at many areas. At theend of the Pleistocene period about 300,000 yrs B.P eustatic adjustment have resulted in a fluctuation of thefollowing order:+5 to +6 m around 0.3 my B.P+1.5 to + 2 m around 0.15 to 0.1 my B.P- recurring periods of decrease between 80,000 and 40,000 yrs B.P. Between 30,000 - 18,000 yrs B.Pa fall of -120 m.- from Holocene period to present level by 2000 to 1000 yrs B.P a progressive rise.Estimates for the global sea level rise in the past century range from 0.10 to 0.15 metre. For theIndoPacific region Bernett calculated that the sea level rise almost doubled over the period 1920 - 1980,compared to the 50 years before. During that period the major factors responsible for the sea level fluctuationwere waxing and waning of the glaciers, compounded by isostatic correction and even tectonic effects incertain parts. In Mauritius, shoreline changes are attributed to both natural phenomenon as well asanthropogenic effects.3.1 NATURAL PHENOMENAA list of natural factors that may contribute to such changes are:(a) Tectonic(b) Eustatic(c) Isostatic rebound(d) Volcanic(e) Biologic(f) Sedimentary(g) Climatic(h) ThermicThough most of these factors do not show direct evidence of their contribution to the changesbecause of lack of investigation and monitoring, their direct relationship do not seem farfetched. These factorshave been invoked for later studies and investigation.Tectonic

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 46Mauritius, being a volcanic island with many episodic manifestations since the Pliocene period tillsome 25,000 yrs B.P and the north easterly movement of the crustal plate, the tectonic factor should be lookedinto. Though tectonic movements have invariably affected the structural setting of Mauritius such as fracturepattern of the rocks, orientation of volcanic vents. crators, ridges, minor fault system, yet, their effect on thepresent sea level fluctuation has to be investigated.EustaticThe melting of the glaciers has been accepted as the most prominent and determining factorcontributing to sea level fluctuation. The direct correlation of the volume of glaciers melted to the increaseof the sea level is not a straight forward calculation. Various factors should be considered to determine thefluctuation level such as isostatic correction, any subsidence of the area, sedimentation rate of the region, etc.Montaggioni (1979), based on a study of radio carbon dating of coral samples suggested episodic sea levelvariations from a sea level of -3.5 m with respect to its present position around 4500 yrs B.P. The averagesea rose to attain its present level between 2000 and 1000 B.P.For Mauritius the established information from Mauritius Meteorological Services as reported by theNational Climate Committee (1991), the annual sea level rise is 1.2 mm. This rise is inducing 0.5 to 0.75 ofcoastline changes on an average, though this figure has to be adequately verified.Isostatic ReboundIsostatic rebound is the natural correction and relief of pressure exerted on the crustal portion duringany orogony, sedimentation or piling of matter on glaciers. For the Mauritian case after the volcanic periodswhere the piled up lavas formed the island of Mauritius with numerous prominent mountains, the erosion andthe planation of these mountains may influence the isostacy of the earth crust. That is to say there might bean adjustment of the land mass and the change in the sea level which is being noted, is in fact higher inmagnitude, but different rate is being experienced. The rise in the sea level should be connected with ,relative sea level rise. Similarly, the weathered and eroded terrigenous materials that have been dischargedon the coastline may also affect the isostatic balance. A thorough scientific investigation should be undertakento correct any such anomaly when computing rate of sea level rise.BiologicIt has been observed that all the coastal segment in front of a pass have undergone serious erosion.That is the coastline has retracted at places by at least 5m landwards. Coral reef is a dynamic system, growingand rising with the rising sea level in ideal conditions. This system intrinsically controls sea level fluctuations.Transgressions of sea level have been indicated by the presence of rubbles of Acropora sp. about 1 km inland.Many indications have been obtained on fluctuation of the coastline where the reef system were sick anddebilitating. Conversely, if the rate of sea level rise is fast and the rate of coral growth could not keep pacewith the rising sea water, the coral reef would be submerged, thus increasing the influence of water levelfluctuation.SedimentationSedimentation process in the coastal zone is perhaps the most dominant factor contributing to thecoastline changes. The case of Rodrigues could serve as a vivid example on this aspect. The Rodrigues lagoonis hypersedimented with terrigenous sediments, derived from the weathering and erosion of the hilly terrain.During mean water mark the lagoonal bed is subaerially exposed. There is a natural shifting of the coastlinelandwards.In Mauritius, because of the good land conservation practice on the hilly terrain, very littleterrigenous amanations are noted. At Maconde a moderate accretion has given rise to evidence of coastlineregression. The reef system being less productive, an insignificant amount of calcareous materials areproduced and with the ever increasing mining of lagoonal sand, the sedimentation effect, in Mauritius vis avis coastline changes is severe. The coastline which are near the reef system especially in the Southern andEastern section is presently very deficient in beach deposit. Part of the sands that had been accumulated anddeposited as beach and dunal deposits have been washed either alongshore or seawards. Such removal ofbeach materials have caused a sea level fluctuation.ClimaticMauritius and its outer islands are often under the influence of tropical cyclones and anticyclonesthat have devastating effects particularly on the coastline. The rise in the water level with low pressure and

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 47the terrific gusts of 225 to 250 km per hr often raises the water level to 2.50 m and the wave uprush to 50 min many parts of the coastline is not uncommon. The scouring of the beach and ridge alter the coastlineconfiguration and the ensuing beach line shifts 5-6 m inland. In 1988, the Belle Mare coastline receeded toabout 5 m, forming a scarp of 1.8 to 2 m. The coastline at Pomponette, during the past 5 yrs retracted to 5 mand the recession is about 30 cm yearly with the planing down of the ridge. The storm waves in generalerode the beach deposit and swells, in the form of constructive waves, reinstate the degradation area.However, in Mauritius there are exemplary indications of beach erosion and coastline changes. Most of theeroded scarps have not been recouped.ThermalClimate change in the form of global warming is felt throughout the world. Consequently, with a risein the sea water temperature, i.e thermal expansion of the sea, there is a corresponding change in theshoreline. Air temperature as well as sea temperature seem to have risen in the past century, as the 1980decade has been particularly warm. This phenomenon has to be thoroughly investigated to compute the rateof the sea level fluctuation.3.2 ANTHROPOGENIC FACTORSStructuralFrom fear of being assaulted and inundated by sea waves, many people residing on the coastal zonehave attempted to ward off this threat by the construction of coastal defences such as seawalls,revetment,jetty, groynes, breakwater, rip rap etc. Most of these structures, in the Mauritian context, are eitherunwarranted or ill designed as they are inducing unparalleled beach erosion at and near them. In Mauritius,a recent survey has revealed that there are more than 200 jetties / groynes that have been illegally constructedon the beach. In the region of La Preneuse and Pointe d'Esny, the coastline is riddled with many ill designedgroynes that are not only an eyesore but are causing more harm than good to the coastal stability. They arealso obstructing passage along the coastline. Instead of arresting sand, most of these structures are depletingbeach deposit, and hence inducing coastline changes. As groynes entrap sediment from the updrift portion,the downdrift one has always a deficit sand budget and the spacing, dimention, orientation and theirimpermeable nature render their function baneful. The misorientation of jetties at Le Morne Brabant Hotelhas triggered serious coastal erosion with a shoreline retreat of about 4 m in 4 years. A good segment of thecoastline of Mauritius looks like a fortress, with prominent sea walls constructed to ward off marine incursionand prevent backshore erosion. Because of the improper engineering design, most of these sea walls are eithercrumbling down or accelerating beach erosion. Being mostly vertical in nature and without any rip rap at thetoe, at all these sites the beach deposit has been washed away due to wave reflection and littoral drifting.During mean sea it is practically impossible to walk along without wetting one's feet. At the regions of Pointed'Esny, Flic en Flac and Le Cannonnier, the HWM is hitting against the sea wall at 1 - 1.2m above the seabedsurface. There is a shifting of shoreline of 5 - 8m at these junction from their date of construction (between10 and 15 years in most cases).The worst repercussion of the sea wall is the impact of wave action on the adjacent coastline. Manyexamples and evidences abound the coastal history where the deflecting waves have scoured the adjacentcoastline and caused a retreat of 5 - 8m. e.g At Belle Mare, near St Geran Hotel, At Flic en Flac near PearlBeach, La Preneuse, Trou d'Eau Douce. Other structures that are affecting the coastline changes areconstruction of coastal road on the backshore or coastal ridge, and on coastal wetland, e.g Grand Baie,Maconde, La Prairie; blocking of natural drains and tidal inlets on the coastline, e.g Grand Baie to Pereybereregions, and construction of sand landing platforms, e.g Roches Noires.Sand MiningInlandDuring the past twenty years sand has been mined from dune and coastal ridge for constructionpurposes and also for the CWA filter beds. The major mining sites were: (Fig. 5)(1) Pereybere(2) Flic en Flac(3) Les Salines(4) Bel Ombre(5) Beau Champ

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 48(6) St. Felix(7) Riviere des Galets(8) Pomponette(9) Pointe d'Esny(10) Poste La Fayette(11) La CambuseAt all these sites beach erosion has been noted but the site Pomponette is most seriously affected.Here sand have been mined from the dunal ridge adjacent the beach and coastal retreat to the tuneof 4m during the past three years have been measured. Because of coarse, spherical and unimodalnature of the sediment influenced by very strongwave current and wind energy, erosion is sopronounced that a coastal strip of 3m is all that is left to protect the backland. Once this bundlikestructure is breached, the coastal road and hundreds of acres of sugar cane plantation would be overflooded.At such sites there is no exchange of sediments from the beach and backshore to the dunal ridge byonshore wind as filtrate deposits and from the ridge to the beach as feedback deposits. To attain thenew equilibrium, part of the sediments that have been mined from the ridge is compensated bywithdrawal from the beach deposit, with the result that beach erosion is accelerated.LagoonalMining of sand from the lagoon is presently undertaken at Pointe d'Esny, Pte des Regates,Mahebourg, Deux Freres, GRSE, Roches Noires, Pte Lascar and Poudre d'Or. The seabedtopography have drastically been changed; needless to say that the coastal ecosystem together withthe marine organisms and habitats have been gradually annihilated. The mining of sand at Pte d'Esnyis seriously affecting the coastline of this area. Similarly beach deposit at Roches Noires has reachedto a point of non recognition. At some segments the coastline has retreated to about 8m during thepast ten years.Planation of DunesIn Mauritius, unfortunately most of the coastal hotels have been constructed on the dunes. Theplanation of the dunes upset the equilibrium and reactivates sediment dynamics, thereby impacting negativelyon the foreshore and backshore. Recently, the coastline at Tropical Hotel at Trou d'Eau Douce experiencedsevere erosion. At one spot during rough sea last year the coastline retracted to 5m. No sediments could becompensated for the loss during scouring by wave action. The foundation of the nearest building was exposedand would have been undermined and the building collapsed if no structural protectionwere undertakenurgently.Presently, Berjaya Hotel which has been constructed on a dune system is experiencing similar fate.Here the dunal deposit has been levelled and pushpiled on the beach, to extend the beach area as undertakenby Beachcomber Group for Shandrani Hotel at Le Chaland. Severe beach erosion is being experienced andsignificantly, the decrease in the height of the dune would allow storm surges during cyclonic conditions toovertop this coastal ridge. The position of the HWM is gradually shifting landwards

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<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 50and with further incursion on the levelled dune a concomitant marine transgression with coastal retreat wouldbe inevitable.Opening of PassesIn order to facilitate boat movement outside the reef, the reef gap are widened. Such opening changesthe hydrodynamic regime, causing a strong current to reach the shore. The expended energy remove a goodchunk of the coastal deposit at that particular spot, causing shoreline retreat, e.g Poste La Fayette and Flicen Flac.4. EFFECTS OF SHORELINE CHANGES4.1 AGRICULTUREThe coastal zone supports a number of agriculturalists who lead their subsistence by undertakingagricultural activities, particularly plantation of vegetables. Reclaimed tidal flats, flood plains, coastal ridgeand sand flats have been cultivated since the last hundred years. The rise of the sea level would overflood thelow lying areas and affect the higher grounds through salt spray and storm surge. This would seriously affectagricultural production and means of subsistence. Production of garlic, onion and solanaceous crops that growwell on the sandy soil would be most impacted. The area that would be affected are Belle Mare, PointeLascars, Bel Ombre, Ile d'Ambre, Roches Noires and Poste Lafayette.4.2 STRUCTURESWith the rising sea level many hotels and campements that have been constructed near the coastlinewould be either inundated or undermined of their foundations. Hotels such as Berjaya, Meridien, Pearl Beachare most vulnerable. Overflooding of the coastal roads at Maconde, Le Morne, Mahebourg(Riviere LaChaux), Poste La Fayette is a common event even during very minor climatic upheaval. Some sections ofthese roads are collapsing. Coastal defences such as sea walls at Riviere des Galets, Flic en Flacq and Pointed'Esny are getting damaged by storm surges.4.3 TOURISMAs the tourist industry depends heavily on hotels and associated infrastructures and as most of thehotels are built right on the dunes, fluctuation of sea level will seriously impact on this sector. Beaches haveto be reprofiled, protection to beach front to be effected, slipways, jetties and groynes to be redesigned anew.Treatment plants and other infrastructures have to be shifted landwards and possibly many coastal roadsdeviated.Socioeconomic impacts would be quite serious through the displacement of coastal communities andwith the change in their mode and pattern of subsistence. In fact the whole system would be disrupted.4.4 AQUIFERThe increase in the sea level would shift the fresh/salt water wedge landwards thus affecting thequality of the coastal aquifer. Overflooding of the backland during adverse climatic conditions would alsocontaminate the coastal freshwater. Such incidence would have a serious bearing on the coastal water quality,agriculture and irrigation. The borehole at Rouge Terre, Fond du Sac is only three km from Grand Baie andthis may be contaminated by saline intrusion as at Grand Baie. This problem would be compounded bytapping water in boreholes near the coastlines.4.5 CHANGE IN ECOSYSTEMCoral and coral reefsCoral population are affected by salinity changes, turbidity, oxygen concentration, temperature andsunlight. A rise in the water level, if the environmental conditions are optimum, would favour coral growth.If the rate of the rise of the sea water level is very high and coral growth could not keep pace with thischange, they might get drowned. Such rise in the sea level would also accompany turbidity with the washing

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 51and entrainment of terrigenous sediments.The rise in the sea level is a consequential effect of global warming. The sea water temperatureowould exceed the 30 c which is the upper sustained limit of tolerance and this would upset the coral systemand the associated lives.Retardation of coral growth would increase the incidence of wave action on thebeach, affecting coastal stability particularly in the Eastern, Southern and South Western and Northernregions.EstuariesEstuaries and estuarine lives are closely interlinked with the marine regimes. An increase in the sealevel would further drown the land adjacent the estuarine mouths, causing a change in salinity and migrationof the estuarine organisms. Alluvial and terrigenous deposits would be reworked and resuspended thusincreasing turbidity. The tidal flats that harbour an array of estuarine and marine organisms would beseriously affected. With he overflooding of the Terre Rouge River tidal flats, the thousands of migratory birdswould perhaps have to find other sanctuary. Salt Water intrusion, particularly near the river mouth, will giverise to much economic problems.Coastal wetlandsThe coastal wetlands has been functioning as flood regulator, sediment and toxic element trap, watercleanser, energy storage and important habitat for many coastal organism. These features have a directbearing on the state and health of the adjacent marine ecosystem. With a rise of the sealevel all the coastalwetlands, which communicate with the sea through tidal inlets would be seriously affected. Not only thewetland ecosystem would be upset but also the marine ones. At Grand Baie and Perebere regions more thantwenty five hectares of wetland would be overflooded with a rise of the sea level by 30 cm (Fig. 6).MangrovesBesides being a nursery ground for many planktons, and juvenile crustaceans and fish, mangrovesentrap terrigenous sediments and act as a very effective coastal protection. As mangroves are susceptible tosalinity changes, this mangrove ecosystem would be affected by the rising sea level.Mangrove state and vitality are not healthy since they are disappearing gradually. Man, with hisinterference on this ecosystem, has created many environmental problems including production. Mangroveswamps would decrease further and this would have a negative bearing on coastal ecology as well as on foodproduction and economy. The various mangrove rehabilitation programmes undertaken in Mauritius andRodrigues would have to be reoriented with new strategies taking into consideration the increase in the sealevel.Fish FarmsCoastal fish farms commonly called barachois would be flooded and its extent would increase.Unless redesigned the walls would collapse and most of the fish would be in the open sea. The rising seawould scour soil from the upland and these would be deposited in the barachois. Many organisms inhabitingthese bararchois would be affected.Incidently oyster beds, crab habitats etc would also have an incidence with the sea level rise.4.6 SAND MININGLagoonal sand mining would be slowed down. Presently the deposits that are subaerially exposedor that are covered with less than 1m water are exploited. With the rising sea only those sites near the beachwould be available for mining. Since the present mining regulations require a set back of 500m from the

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 52HWM, practically no site would be available, unless the set back is decreassed. If this is allowed f21

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 53the adjacent beach would suffer further degradation. Unless coralline sand are substituted by basaltic sand,or mining in the deep sea with dredgers, availability of coralline sand would sensibly decrease, causing a slowdown in the construction sector.The ex sand quarries such as those of Pomponette, Pointe D'Esny, Riviere des Galets, St Felix, LesSalines and Poste La Fayetter would be overflooded and those colonised with grasses and trees would bedestroyed.4.7 SALT INDUSTRYMost of the salt pans that are constructed on the coast would be overflooded and during slack tideseawater would still be retained. The salt pans should have to be shifted upland. Salt pans at Les Salines thatobtain sea water during high tide would be ruined. There is a likelihood that the salt prodcued would becontaminated, especially at Riviere Noires.4.8 COASTAL INDUSTRIESThose few coastal industries that lie near the HWM e.g. Bel Ombre Sugar Factory, Tuna Canning,Power Plants of Fort Victoria and Fort Georges, MCFI, Cement Bulk Terminal, textile factories such as thoseat Ile D'Ambre etc would be affected. The access roads, underground storage tanks, waste water disposalsystem would be damaged, causing much harm to the environment.4.9 HARBOUR INFRASTRUCTURE AND SERVICESThe Port Louis area which is the business centre for the island is more or less flat, rising a few metresamsl. The harbour area has been dredged and reclaimed and many important industries has been implantedsuch as power station, MCFI, oil storage tanks, Bulk Sugar terminals, Grain Milling, fish processing etc.During rough seas water splash over the quays and overflooded the adjacent areas.The various infrastructures such as roads, quays, platform, docks, stores, oil pipes, sewage pipes etcwould be affected. These infrastructures facilities and services would have to be reviewed and planned takinginto consideration the upper reaches of the sea level.4.10 SALINE INTRUSIONWith the rising sea level the fresh/salt water interface would move landwards. The abstraction offresh water in the coastal regions would no doubt increase saline intrusion. Agriculture, irrigation, potablewater and many industrial activities would suffer. In some regions of the north saline intrusion is beingobserved (Fig. 8). Concurrently decrease in lens size of the aquifer though flooding of sea water during stormand cyclones would incidentally impair water quality.A comprehensive study is warranted to determine the extent of salt water intrusion that is expectedwith the different scenarios of the rise of sea level. This study would be useful to prepare a proper resourcemanagement plan for water utilisation and development.4.11 COASTAL WATER POLLUTIONCoastal solid waste disposal systemPresently two official dumping grounds exist near the coast- one at Roches Bois and the other atBois D'Oiseaux, Poudre D'Or. There is a very likelihood that the rising sea water would wash the wastestogether with the leachates and polluting the coastal water including the marine organism. The aquifers andthe barachois would be contaminated, thus posing a real health threat. The Roche Bois dumping ground hasbeen decommissioned and very soon that of Poudre D'Or would be sealed off, with the creation of acentralised dumping ground at Mare D'Australia.Sewage outfall

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 54With the reclamation of the sea at Ruisseau Terre Rouge in 1991, the flushing of the sewer outfalldecreased drastically and raw wastes could be seen deposited all along this part of the coastline. Themanifestation of eutrophication is also related to this problem. The sewage outfall would have to beredesigned and extended, involving heavy investment.There are no doubt many coastal hotels and bungalowsthat dispose of their sewage wastes through septic tanks and absorption pits. The rising sea level wouldcontaminate the ground water and the coastal water, posing threat to the health of the coastal community.A coastal development plan would have to be prepared to identify appropriate sites for major coastaldevelopment. It is in this context that for all major coastal development projects an Environment ImpactAssessment is required to predict and mitigate associated environmental problems.Coastal landAll the coastal land from the HWM to 81.21m landwards belong to the state, except at somelocalities. Most of these lands are leased either for hotel development or for bungalows. The land from theHWM to the low water marks and the public beaches are meant for the public use. Consequently, with therise in the sea level the HWM would shift further landswards and this could give rise to many legalcomplications.For example the management of one hotel at Flic en Flac has constructed a sea wall on the HWMsome years ago. With the rising sea and with the reflection caused to waves this water level has transgressedlandwards. During mean water mark the sea water strikes the food of the wall and during high tide the seais 60-70cm deep. The management claims that during the construction of the seawall he had left the requiredset back but due to natural phenomenon the water level has risen. Presently it is impossible to walk along thebeach.According to planning guidelines new development plots on the seaward side shall be at least 300m².With the rising sea the requirement of this plot size or the set back could not be met in some cases.5. CONTROLLED MEASURESThe effects of sea level rise is giving rise to many complicated problems that could only be addressedby judicious planning, redesigning of the existing protections and adaptation strategies.5.1 PHYSICAL CONTROLStructuralSeawallIn order to protect the beach front and the adjacent properties many structures have been put up andmost of which are not giving the targetted results. Such structures have to be dismantled andredesigned. It is imperative that during their dismantling, care should be taken to remove them phasewise or the stability of the adjacent system would be upset as the case of Pointe d'Esny, when theremoval of one groyne caused severe erosion of the beach and the collapse and cracking of theadjacent sea wall.Where the beach is getting eroded a scientific investigation should be undertaken to identify thefactors effecting erosion, wave climate, hydrodynamic regime and sediment disposal pattern. In mostof the cases it is recommended to use either an inclined sea wall with appropriate batter angle anda rip rap of the toe or gabion wall that effectively dissipate wave energy and increase deposition. Areno mattress at the foot and a geo textile screen behind the gabion wall should be placed to preventrilling and collapse of the village.GroynesIt is recommended that groynes should be constructed where there is adequate sediment drift. Thesegroynes should be designed by competent coastal engineers. Their length, orientation and heightshould be properly calculated. All these groynes should be of permeable nature so as to interceptsediments from both sides during change in current direction.

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 55All these groynes that are misoriented and missited should be redesigned and also made permeable.There are quite a few groynes especially in the Black River Coastline that are mere rock dumps.They are very bulky and massive and of undue length. These structures should also be modified tomake them function effectively.JettiesJetties like groynes have been constructed in a very haphazard manner. Most of them are inducingerosion, and are blocking passages along the beach. These structures have to be corrected. Newjetties should be properly designed by a competent engineer and should necessarily be on piles. TheMinistry of Environment and Quality of Life recommends jetties only where they would be requiredand their designs should be as per the Ministry's specification.Soft ProtectionWhenever possible soft protection should be undertaken in the form of artificial beach nourishment,sand bags, tyres, etc. For artificial beach nourishment care should be taken to place sands of appropriate grainsize and declivity. In the first instance the newly deposited sands should be protected from wave action tilltheir complete stabilisation. In such cases granulometric analysis, slope and hydrodynamic studies arerequired.Vegetative ProtectionVegetative cover afford a good protection against erosion. The beach and ridge scarp that has beeneaten up could be reprofiled and colonised with grasses and managed. Salt tolerant trees, such as filao, boismanioc, bois matelot, velontier could be planted as a screen on the high water mark fringe to prevent erosioncaused by wave and wind action. Mangrove plants could also be planted in these areas where these plantscould thrive well.However, management of such plantation in the form of recruitment, watering, protection againstfire, trampling, grazing by animals are of extreme importance.Sand MiningSand Mining from the dune has been stopped and no permit is granted. Mining from the lagoonshould be restricted and only those areas should be exploited where sands are accreted. In the long run miningfrom the lagoon should be banned and coralling sand should be replaced by basaltic ones.Control of Pollution from Landbased SourcesCoralline sands are mainly detrital products of coral, tests, spicules, bones of other marineorganisms. In order to control sea level fluctuation and beach erosion the health of the lagoon with theinhabiting marine lives should be enhanced. Consequently, pollution from land base sources should becontrolled through treatment plants, process changes and good management practice.Green House GasesThe emission of green house gases in the atmosphere is the major factor contributing to climaticchanges and sea level rise. Use of alternate source of energy, decrease in the utility and ultimatelyban of the CFC, and other green house gases and reafforestation could in the long run alleviate globalwarming and sea level rise. Such action should be taken at international level and all the countriesshould be united as one nation and take concerted action against this problem.Mauritius is a developing country under the definition of the Montreal Protocol with a per capitaconsumption of 0.07 kg of Ozone Depleting Substances (ODSs) per annum. With growing concerntowards environmental protection the Government of Mauritius signed the Protocol in August 1992and ratified the same in November 1992. This act reflects the intentions and commitment of theGovernment and People of Mauritius to join the international efforts to save the Ozone Layer bycomplying with the Protocol.As per the terms and conditions of the Protocol, the consumption of Ozone depleting Substances

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 56(ODSs) is required to be phased out from a level of the average consumption in the years 1995,1996and 1997 by the Year 2010 or 2015 depending on the substances.5.2. PLANNING CONTROL<strong>Planning</strong> instrument is an important tool to address and accomodate the environmental effects causedby sea level rise. With the rise of the sea level many areas would be flooded, industries, houses, landresources and other economic activities affected it would be wise to plan out and relocate coastal activitiesand enterprises in areas that would have little effect with such changes.One of the most important parameters that would have to be considered is the provision of thesetback. All the industries, buildings and infrastructures on the coastal zone should be at appropriate distanceand position. The set back should be site specific taking into consideration slope, altitute and sensitivity ofthe area.Only such industries should be placed in the zone that will not cause any significant environmentalproblems with the sea level rise. In order to regulate such developmnent the Ministry of Environment andQuality of Life is preparing an Environmental Sensitive Areas Map with guidelines on nature and type ofindustries and development that could be allowed in such areas.All major developments should be allowed on site beyond the reach of the extreme scenario of sealevel rise. Some other developments should be retreated from the island.Incidentally for the major houses on any other structures a good engineering design should be madetaking into consideration wave and sea water uprush during rough sea. Structures on piles should be givendue consideration.Wherever retreat or relocation is not possible, an adaptation strategy should be developped. Theexisting structures and facilities should be curtailed to adapt to the present situation and when such practiceis not feasible it would be wise to retreat.6. RATE OF SHORELINE AND BATHYMETRIC CHANGESUntil recently no systematic investigation was undertaken to determine rate of coastal erosion andthe factors affecting them. Coastal erosion is a phenomenon where there is a complex interplay of variousnatural forces on sediment distribution and dispersal. Many physical parameters are involved and in order todetermine effectively the factors affecting such degradation, an indepth scientific investigation is warrantedand this might take several years to come to a conclusion. It is possible to identify these factors but in orderto correctly recommend the mitigative measures, particularly structural protection, a thorough investigationof the impacts of the prevailing hydrodynamic conditions, depositional energy regime on sedimentcharacteristics is extremely important and for such studies many cyclic observations and monitoring forseveral years should be undertaken. In mauritius coastal erosion problem is not new. This phenomenon hasbeen prevailing upon since many years. However, with the tremendous pressure exerted on the coastal zone,particularly with the influx of tourists requiring many hotels and with the high demand of coastal land forbungalows, and utility of coralline sand mined from dune and inshore, coastal erosion has become a seriousconcern for the coastal developers, coastal community and the government.To contain the erosional problems many coastal developers sought the services of local and foreignconsultants and few reports have been submitted to the department of environment on this issue. A strikingcase was that of St Geran where then coastline receeded many metres seawards and a scarp of 1 - 2m wasprominently seen to a distance of 200m in the year 1988. The ridge sediments were scooped out and

f22<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 57

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 58swirled away during the spring tide of 1988 and cyclonic conditions of 1989. The beach face angle flattened5 - 6 % despite the coarse nature of the sands. Regular bathymetric surveys were undertaken quarterly andgeotextile bags and artificial algae were placed along and across the beach in the form of groynes andbreakwater. The erosional site was gradually rehabilitated and stabilised and presently a vestige of ridge scarpcould be seen.With the dismantling of a groyne at Pte d'Esny in 1991, a monitoring exercise was undertaken toinvestigate the environmental problems that ensued. The beach front is protected by a vertical massive stonewall and at its foot a groyne runs across the beach. About 1 m sand was trapped at the heel of this groyne.With the dismantling of the groyne all the sands at this spot got washed away and waves hit directly againstthe sea wall thereby fracturing and also undermining the seawall. The adjacent sea wall collapsed with itsparapet. The promoter was asked to put sand bags in the form of a groyne to entrap drifting sand and threelevelling exercices were undertaken at one month interval. Six points were chosen along the coastline andsix other points at 2m distance were taken. It was noted that after 38 days the beach profile changedconsiderably. At the foot of the wall, 20 cm of coarse sands were deposited. However, at the mid portion ofthe sea wall, 2m from the foot about 5 - 10 cm of sand was washed away. On the third month at the foot ofthe wall all along, a further 20 cm of sand was deposited and the beach profile became near horizontal.A similar beach monitoring exercise was undertaken at St Geran to evaluate the beach equilibriumand environmental repercussions caused by the removal sand bags. Eight stations were established on thedunal ridge and cross profile survey undertaken seawards to a maximum distance of 65m. Three levellingexercise were undertaken on 16.10.92, 23.10.92 And 29.10.92. The results showed that no beach erosion wascaused due to the removal of sand bags. The previous erosion was caused by adverse climatic conditions assuch erosional manifestations were observed all along the coastal segment of Belle Mare. It is worth notingthat station g which is in front of a vertical sea wall gave rise to a concave profile at the foot.All the other erosional sites mentioned in this report are results of visual inspection during varioussite visits and monitoring. The visits were not undertaken regularly and hence no solid conclusions could bederived. Still, it gave an indication of the incidenceof coastal erosion both spatially and temporally.From January 1993, with the implementation of a pilot project on the vulnerability assessment ofselected coastlines of mauritius in the context of climate change and sea level rise, two sites have beenidentified, viz Pomponette region situated in the south and Port Louis harbour area.Theobjectives of this project are:(i) long term- to assist in the project preparation of a long term monitoring programme on coastal and phenomenarelated to climate change and sea level rise.(ii) short term- to examine the possible effects of sea level changes on the coastal environment -toexamine the combined effects of temperature elevations and sea level rise on the terrestrial andcoastal ecosystem- to examine the possible impacts of climatic and ecological changes on coastal human activities andsocio economic structures- to determine areas or systems which appear most vulnerable to the above changes- to increase awareness on coastal impacts likely to result from climate change- to promote multidisciplinary and integrated thinking in the assessment of climate change at the levelof individual countries- to identify and recommend appropriate policy options and strategies to mitigate the likely negativeimpactsMethodology- contour interval of 1 m were taken for the preparation of a 1 m contour map. L-sectionsa t

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 59variouspoint sweretaken toobtain amoresensitiveindicatio no fthetopograph yo ftheterrain.Lsectionswerealsotaken inthelagoon.Methods ofsurvey- Most of the new roads on the former sand quarry sites were surveyed graphically. The plane tableself reducing alidade was also used to that end.- However, control had to be provided for the survey of the unmapped region and the riviere des galetshousing estate. A long traverse was observed from ttp 17 (pomponete) to TTp 16 (near Ilot Sanchot).The traverse stations were located along the main road (89) and were iron pails hammered in the roadtarmac. Angles were observed.LevellingOnly 2 BMG's were found in that region and from these levelling loops have been observed to allthe traverse stations found along the road B9. These loops were carried out at a tertiary level with a WildAutomatic Level. Spot heighting within the filao trees on the Pomponette Public Beach was carried out using

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 60the Wild RDS. Difficulties were encountered while pointing to staves within the filao trees. This same methodwas also used while levelling within the Riviere des Galets Housing Estate and Pointe aux Roches Villas. Thelandward area (e.g. the former sand quarry of Pomponette) were levelled by means of the Automatic WildLevel at every road junctions. All the spot heighting loops started from and ended on a point of known level.Ten L-sections lines were identified and levelled using a Wild Automatic Level. Two Bench Markshave been cast in each L-Section line so that the same L-Section may be produced seaward.PlottingPlottings have been carried out on PFD as far as details are concerned. Spot heights were plotted ona proper plan and contours interpolated on it. These PFD's and contour plans were mounted and then tracedon a permatrace to produce the final plan at the scale of 1/2500. L-Sections have been plotted at the scaleof 1/1000 horizontally and 1/50 vertically.Topographic, bathymetric, ecological and land use survey and oceanographic data collection andsedimentological analysis are undertaken. Change in the coastline, bathymetry and depositional pattern wouldindicate fluctuation in sea level rise quantitatively and the factors contributing to coastal erosion anddeposition. The survey exercise and data collection are ongoing till end of 1994, after which a conclusivereport would be submitted on the problems related to sea level changes and control measures to beundertaken. The accretionary nature of the beach and its stability are due to the presence of the dunal sandreserve. The erosion of the beach by wave action has been mitigated by the influx of dunal sediments, so thatthe vestige of the beach scarp is being obliterated. As long as this deposit is not depleted or disturbed thecoastal zone at this segment will be protected.It should also be noted that at this coastal segment there is a strong onshore/offshore wind regime.Even though the dunal sediments are fine size they have been completely arrested.The exchange of sedimentfrom the beach to the dune through the backshore as filtrate deposit by onshore wind and their redispersalfrom the dune to beach as feedback deposit by offshore wind has been more or less stabilised. Any scouringor mining of this eolian deposit will disrupt the whole setup of the coastal system at this region.The shape of the dune with the characteristic angle of the limbs is the deciding factor of itsstabilization.The angle of repose of the grains is not a haphazard setting,but a harmoniuos balance betweenenergy regime and sediment enertia. The levelling of this feature will bring about an unstability in the wholesystem affecting the coastal zone including the lagoonal and reefy areas.This dunal deposit is also acting as a barrier against high energitic sea waves ,spring tides and saltspray that are invariably affecting the upland, including vegetation and coastal aquifer. This feature, besidesacting as energy stabiliser, is a resting, breeding and nesting ground for many coastal faunas particularlybirds.7. NATIONAL POLICY ON COASTAL EROSIONThe coastal zone is an area where there is a complex interplay of various energy regimes on a tristatesystem, i.e land, water and air. These energy regimes converge to give rise to a dynamic ystgem where thephysical and depositional features are always trying to attain an equilibnrium with the energy flow. Very oftenacceleration or dominance of one energy force either due to natural or anthropogenic interference upset theequilibrium with consequential disastrous upheaval.Being under constant stress either by natural forces or human needs, the coastal features and relateddevelopment undergo profound changes that could not be reinstated or retransformed. It is precisely becauseof these changes that the discreet facets of the whole coastal ecosystem that were harmoniously bound by thedifferent energy levels are gradually being defaced, gradually rendering them and dismal liability to humans.By virtue of its natural attributes such as sites for residences, industries, vegetation, ecology, food and energyproduction, tranquility, aesthetism, stabilising factor, recreational and because of its limit it is in the interestof each and every nation who has been endowed with this resource should sustainably developm this zonewithout imposing undue pressure.Taking into consideration the size of Mauritius with limited land resourcesand a prolific tourist industry that depend a lot on the good beaches and clean lagoon, every effort is being

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 61made by th eState to restore the natural attributes of this zone and protect and preserve its characteristics.Some of the measures taken are :7.1 PLANNING CONTROLFor the optimal and sustainable use of the scarce land resources the Government of Mauritius hasprepared a National Development Physical Plan wherein a fairly detailed planning strategy has beenelaborated for the preservation and conservation of the coastal resources. Under the overall context of theNPDP outline schemes have been prepared in details wiht appropriate guidelines for coastal development.Under the Outline Scheme a Northern Tourist Zone plan has already been prepared and two such plans forthe south-western zone and the north-eastern zone would soon be embarked upon.All development undertaken within the coastal zone on the landwardside require permits from theplanning authorities. The projects submitted are rigorously reviewed and evaluated prior to consideration. Thecoastal strip which is mainly used for recreational touristic and residential purposes have been furthersubdivided into two portions.(a)Portion 1 comprises the lands fringing the shore and because of ts sensitive nature development isassessed and allowed on the opportunities and constrain of the site.- development density, building height, setback form the sea, siting of septic tanks, construction ofjetties and other structures need the approval of various ministries.- dredging, sand mining, removal of beach rocks, dumping of material at the sea or on the beachrequire clearances from various ministries- sensitive areas such as wetland, mangroves, water courses, nature preservation zones are generallyprotected from development(b)Portion 2 extends from behind portion 1 from the coastal road inland. It is also under great pressure.Guidelines for development an this portion are generally less strict than in portion 1 but neverthelessaim at encouraging economic and orderly use of land, attractive in its setting and acts as a bufferalong the coast.7.2 SETBACKAll new developments on the coastal zone require a minimum setback that should be scrupulouslyobserved. This buffer zone absorbs pressure exerted from marine environment as well as land based pollution.Siting of residential and hotel complexes with connected septic tands and sewage tretment plants requiresconsideration of slope, altitude, sensitivity of area and nature, type and size of structures.For all such development extreme scenario of sea level rise, pressure drop, maxim;um amplitude of sea wateruprush, structure, grainsize, slope adn roughness of coastlne are considered, Similarly statutory setback formwater courses and even additional safety values are added for many development.However, all existing developments are allowed to stay in situ and practical precautionary measures areundertaken to minimise any harm caused.7.3 ENVIRONMENTAL IMPACT ASSESSMENTIn order to identify environmental problems and address them at the initial stage of a proposedproject, so as to render any development sustainable, the Environment Protection Act of 1991, assubsequently amended in 1993 requires a proponent, whose project is a scheduled undertaking, to apply foran Environmental Impact Assessment Licence. The following coastal development projects are included inthe scheduled undertakings:(i)(ii)(iii)(iv)(v)(vi)Wetlands developmentCreation of islandsRemoval of sand, coral, beach rock or natural vegetationSand crushing, screening and washingMining of sand dunes and seabedsLagoon dredging and reprofiling of seabeds

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 62(vii)(viii)(ix)(x)(xi)Modification of existing coastlineMarinasConstruction of jettiesBarachois developmentParcelling out of land into 10 or more lots in the coastal zone.Any of the above projects are published in the Government Gazette as well as in two dailies invitingpublic comments on the proposed project. It is then sent to various enforcing agencies who have a concernin the project for views. The Director of the Department of Environment reviews the E.I.A and sends hisreview with any public comments to the E.I.A Committee. The latter further examines the Director's reviewand the public comments and accordingly recommends to the Minister for approval. The different phases ofscreening, reviewing and assessing the E.I.A report render the development fullproofed. All anvironmentalparameters connected with the project are properly examined and considered and with the EIA Licence, aset of environmental conditions are imposed upon the proponent to mitigate any nuisances caused from thedevelopment. In all the cases, implications of sea level rise and marine and coastal pollution are invariablyconsidered.7.4 ENVIRONMENT SENSITIVE AREASIn order to effectively control development on the coastal zone and manage the land resources theMinistry of Environment and Quality of Life has embarked on the preparation of an Environmental SensitiveArea Map that could serve as a guide to future coastal development.Features such as beach, dunes, coastal wetland, mangroves, coral reefs, sea grasses, estuaries are verycritical areas that warrant serious protection. In these areas no development would be recommended exceptthose concerned with conservation purposes.7.5 POLLUTION FROM LAND BASED SOURCESThe sea is a receiving media for most of the land based pollution. Control of pollution from thesesources would have a positive bearing on the coastal and marine ecosystem. The improvement andenhancement of lagoonal health can, to a certain degree, mitigate the negative impacts of sea level risethrough increasing the vitality and growth rate of coral reef and production of detrital coralline sands.The Ministry of Environment and Quality of Life in collaboration with other Ministries are in theprocess of finalising the effluent limitation standards that would regulate the discharge of effluents in watercourses including the lagoon. Incidentally as per Section 33 (2) of the Environment Protection Act 1991, theMinister may establish different standards for water quality having regards to the use and value of water fordomestic supplies, propagation of fish, flora and fauna, and wild life, recreational purpose, agricultural,industrial and other uses. Action is being taken to this effect.7.6 NATIONAL COASTAL EROSION RESEARCH STRATEGYIn addition to the various legislations enacted to preserve the natural characteristics and integrity ofthe coastal ecosystem, various strategies have been identified and adopted by the State. Two years before,a South African Team of the Division of Earth, Marine and Atmospheric Science and Technology(EMATEK), the Council for Scientific and Industrial Research (CSIR) was invited to:(i)(ii)(iii)(iv)(v)(vi)Identify the various erosional sites on the coastlineTo determine the degree of severity and determine the factors contributing to these problemsTo prepare short term measures to combat these problems at those sites most affectedTo prepare policy guidelines and prepare a long term coastal management planTo develop sensors and systems for data handling for effective monitoring of coastal climate andsediment transportTo train Mauritian scientists on the above.A preliminary report has been submitted to the Department of Environment, Ministry of Environmentand Quality of Life.Similarly thirteen coastal/marine projects have been identified under the Indian Ocean Commission,financed by EEC and grouping five island states. These projects would be implemented very shortly. All these

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 63projects are interlinked and among them erosion and degradatiuon of the coastline and hypersedimentation,conservation and rehabilitation of the Rodrigues coastline would be given due attention.ANNEX IREFERENCESANON 1989. Tlle Greenhouse Effects: will the coral survive? In: Reflections, April 1989 No.23.ATHERLEY K.A.(1989). Seascape (R) synthetic seaweed. A failed solution to erosion in Barbados. ProcCoastal Zone 89, ASCE.AWACS: Cox and Hudson -Coral Sand Resources of Mauritius and Rodrigues - 1993.BAGUANT B.K. and C.P.FRANCOIS (1991). Institutional collaboration to promote the use ofreplacement construction materials as an alternative to coral depletion. A commonwealth science council- University of Mauritius project under idea programme.BARRATT L. PRICE A. JUDGE T., BHEEROO R.A., GANGAPERSAD D. - Effects of sand miningon lagoon ecosystem - Case study at Roches Noires, Mauritius.BEACHCOMBER LTD(1990). Protection de la plage du Morne Brabant.BHEEROO R.A. AND GANGAPERSAD D., 1989 - 1991 - Reports on Evaluation of marine fauna, floraand sand quantity and quality for proposed coral sand mining sitel of MauritiusBIRD E C E(1983). Factors influencing beach erosion and accretion: a global review. Proc 1st SandyBeaches Symposium, Port Elizabeth, South Africa.BIRD E C F (1985). Coastline Changes - A Global Review. Wiley Interscience, Chichester.BOTT A N. J S HAILEY and P D HUNGER (1978). Wave Power prospects for Mauritius. Proc WaterPower and Dam Construction.BUDDEMEIER R.W. & S.V. SMITH 198S. Coral reef growth in an area of rapidly rising sea level:predictions and suggestions for longterm research. Coral Reefs 7: 51-56.C.E.T.E. Mediterranee, SIGMA {1989). Recommendations relatives a la protection contre l'erosion dela plage de l'hotel- Saint Geran (lle Maurice). ;CHINEAH V. 'GUNGAPERSAD' AND POINEN M.- 1992 - Lagoon Sand Resources of Rodrigues Islandin relation to proposed coral sand exploitation.CROSS W., JUDGE T., BHEEROO R.A., FAGOONA I., GANGAPERSAD D., 1991 - Study for thecreation of radial and circumferential channels in Rodrigues Lagoon.FAGOONEE I. (1989) - Coastal Zone of Mauritius: Sea level rise consideration.GANGAPERSAD D. AND NALLEE M. 1993 - Draft Guidelines adapted for Coastal 2One Managementin Mauritius.HEKSTRA G.P. (1990) - Global warming and rising sea levels the policy implications.HOFFMAN J.S., KEYES D. & J.G.TITUS 1983. Projecting Future Sea Level Rise: methodology,estimates to the year 2100 and research needs. Strategic Studies Staff, US EPA, Washington, D.C.121 p.JOOTTUN L.(1991). Impacts of Inland Sandquarry on the Coastal Ecosystem. Department of theEnvironment, Mauritius.JOOTTUN L. (1988) - Coastal morphology and sedimentation dynamics of Agalega coastline.JOOTTUN L. (1989) - Coastal Survey of Baie aux Tortues with special reference to depositionaldynamics and management of the ecosystem.JOOTTUN L. (1991) - Addressing coastal zone management problems in Mauritius, structural impactsupon beach stability.JOOTTUN L. (1993) - Report on major environmental problem in Rodrigues and proposed solution.JOOTTUN L. (1993) - Monitoring on coastal erosion problems at St Geran, Bellc Mare.Mc INTYRE W.G. and H.J. WALKER (1964). Tropical Cyclones and Coastal Morphology in Mauritius.Am Ass Am geogr. 54, 582-596.Ministry of Environment and Quality of Life (1991). State of the Environment in Mauritius. Reportprepared for presentation at the United Nations Conference on Environment and Development. Rio deJaneiro, Brazil,June 1992.MONTAGGIONI l (1979). Application du principe de Bruun a la determination des variations du niveaumarin au Cours de l'Hoolocene: Cas des iles Maurice et la Reunion, Ocean Indien, MarineGeology, 31, M29-M38.MONTAGGIONI l.& MAHE J. 1980 -Caracterisation faciologique des sediments recifaux de Mauricepar l'analyse factorielle des correspondences. Oceanol. Acta 3 (4): 409-490.

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 64MONTAGGIONI L. & FAURE G. 1980. Les recifs coralliens des Mascareignes (Ocean Indien). Coll.Travaux Centre Universitaire, Reunion.MULLER J. and P. RUCH (1990) - Note sur la demande de permis de dragage de sable corallien dansla Baie de Tamarin cote sud-ouest de Maurice. Universite d'Aix Marseille I, France.National Climate Committee (1991) - Summary Report and Recommendations of Working group on theimpact of climate change on the coastal zone in Mauritius.PADYA B.M. 1984. The climate of Mauritius. MeteorologicaJ Office, Mauritius, 2nd Edition. 217p.PICHON M. 1971. Comparative Study of the main features of some coral reefs of Madagascar ! Reunionand Mauritius. Symp.Zool. Soc. Lond.28: 185-216.QUELENNEC R.E. (1987) - Extraction de sables coralliens et de coraux a l'Ile Maurice: Situation actuele,alternatives et propositions pour la protection et la gestion des milieux littoraux et lagonaires. 87 MUS 138BRGM, Marseille.SAHA T. & S.JUGESSUR 1983. Analysis of wave recordings and the estimation of wave power inMauritius. Proc. National Energy Conference, University of Mauritius. pp.821-832.SALM R. 1976. The structure and successional status of three coral reefs at Mauritius. Proc.RoyalSoc.Arts Sci. Maur.III (2), 227-240.SIGMA (1991,1992) - Beach Protection Scheme at St Geran Hotel. Interim Reports 1991, August 1991,November 1991,February 1992, April 1992.SOGREAH (1991) - Preparation of a Master Plan for the development of the northern tourist zone andthe protection of its seaboard. Report 5.2104 R3 prepared for the Ministry of Housing, Landsand Environment, Mauritius.TITUS J.G. 1986. Greenhouse effect. sea level rise, and coastal zone management. Coastal ZoneManagement Journal, 14 (3): 147-172.TOUE T. and WNAG H. (1990) - Three climensiorlal effects of a seawall on the adjacent beach. ProcICCE, ASCE.

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 65V. SEYCHELLES NATIONAL REPORT COASTAL EROSION, SEA -LEVEL CHANGES AND THEIR IMPACTSBy Nirmal Jivan Shah 11. SEYCHELLES: BASIC INFORMATIONThe Republic of Seychelles is made up of 115 islands scattered over an Exclusive Economic Zonecovering an area of 1,374,000 square kilometres. The total land area is 455 square kilometres (45,250hectares). The islands are situated in the Western Indian Ocean between 4 degrees and 11 degrees south ofthe equator. Mahe is the main island and the seat of Government. 41 islands are granitic and are all foundwithin a radius of 50 km from the main granitic island of Mahe. With a land area of 148 square kilometres,Mahe amounts for one third of the total land area of the archipelago. The remaining 74 islands are alcoralline. The furthermost island is Aldabra 1150 kilometres to the south of Mahe.The population of 68,600 (1987 Census) is concentrated on the three largest granitic islands of Mahe(60,400), Praslin (5,600), and La Digue (1,900). The coralline islands support a population of 300 persons.23,000 of the total population are under fifteen years of age, and Seychelles has recorded an average annualpopulation growth rate of 0.8 percent. The average family size of Seychelles is 5 people. Life expectancyat birth for women and men is estimated at 72 and 68 years respectively. Seychelles is predominantly aChristian country (99%); the main church is the Roman Catholic which covers 88.6% of the population. Ofthe 20,000 wage earners, a total of 2,300 are employed in the agricultural, forestry and fishing sectors, 3,300in mining, manufacturing and construction, 2,500 in tourist related industries, and 7,500 in services(Information has been taken from the last census conducted in Seychelles which was in 1987).In 1903, Seychelles became a Crown Colony of the UK, separate from Mauritius. It gained fulindependence in 1976 as a Republic. Creole, English and French are today the official national languages.The Government of Seychelles is headed by an elected President, with a cabinet of 10 Ministers havingspecific portfolio assignments.2. COASTAL GEOMORPHOLOGY AND CLIMATE BASELINEThe central Seychelles consist of forty-one islands and islets built of Precambrian rockapproximately six hundred and fifty million years old formed from the breakup of Gondwanaland some overhundred and thirty million years ago by tectonic activity. The islands rise from the Seychelles Bank, a shoalarea of about thirty one thousand square kilometres, with depths ranging up to sixty meters. The islands riseto a maximum of 914 meters at Morne Seychellois on Mahe. The granite islands are typically rugged andhilly. The coral islands consist of two types, low sand cays such as Bird and Denis, and elevated reeflimestones such as the Aldabra group. The coral islands are low although sand dunes on some islands mayreach as high as thirty two meters.The coastal zone on the granitic islands consist of elevated terraces known locally as "plateau", aswell as marshy areas. The terraces or plateau which lie up to two meters above sea level consists ofcalcareous reef material which builds up as sand dunes and pocket beaches known as "anses". The sandydeposits have accumulated in the last six thousand years. In contrast low-lying areas around river mouths aremarshy and characterized by sediments of fine clays and quartz. Port Victoria, the capital, is built up on suchsediments. The main island of Mahe is twenty-seven kilometres long and six kilometres wide with a land areaof one hundred and forty-eight square kilometres. The coastline runs about one hundred and five kilometresin length and there are thirty-six kilometres of sandy beaches. The second largest island, Praslin, has acoastline which is forty-three kilometres long and has twenty-one kilometres of beaches. The plateau areaon the islands is small, the largest occurring on Praslin and La Digue. The La Digue plateau covers about onehundred and sixty-five hectares and on Praslin total plateau area is about hundred and ninety- three hectares.1Environment.Resources.Oceans (ENVI.R.O.), P.O. Box 699, Mahe, Seychelles

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 66The climate of the Seychelles is generally tropical and humid with a mean annual rainfall rangingfrom one thousand five hundred to two thousand five hundred millimetres at sea level on the granitics to lessthan one thousand millimetres on the coral islands. Temperature ranges from a minimum of 24 degreesCelsius to a maximum of 30 degrees Celsius. During March to November the Southeast trades blow withgreat constancy south of the equator and extend north of the equator. The trades last for longer periods andblow more strongly in the southern than in northern Seychelles. During December to March the trades retreatsouth and winds are light northwesterly. The trade wind monsoon season is dry and the northwest wet.Thegranitic islands and most of the Northerly coral islands lie outside the cyclonic belt. Warm surface waters(23 to 27C) covers the Seychelles area during the Southeast trades. This is replaced by even warmer waters(28 - 31C) during the Northwest monsoon.The granitic islands are well watered by streams. Exploitation of the upper hill slopes and destructionof natural vegetation have led to a wide fluctuation in stream flow. On the coastal zone, infiltration rate ofwater is high and can take up to five hundred millimetres of rain an hour. However, the watertable can, anddoes rise. On the outer islands a stable bi-convex lens of fresh water is established in the sand. The tidalrange is about one meter in the granitic islands to two and half meters on Aldabra.3. COASTAL ECOLOGY AND SHORELINE CHANGEThe coastal vegetation of the granitic islands has been described by various authors including Vesey-Fitzgerald , Sauer and Procter. Those of the coral islands are described by Stoddart and Fosberg. Thelowland or coastal vegetation has been severely modified by human activities. The plateau on the graniticislands having good and well- drained soils were cleared of forests and planted with coconuts. This has beena major disaster in ecological terms. Mangroves, formerly very extensive, especially on the East coast ofMahe have been progressively destroyed beginning soon after the first human settlement. Small pockets stillremain near open stream mouths. On the western coast of Mahe a continuous belt of mangrove continues toexist in the Port Launay and Baie Ternay Marine National Parks. In Curieuse Marine National Park a welldeveloped mangrove system thrives. Mangroves have recolonised backwater areas created by recent landreclamation between Victoria and the International Airport. Many species have been recorded withAvicennia marina being most abundant. The largest mangrove systems are on Aldabra, Cosmoledo andAstove. Lowland fresh and brackish marshes were formerly found behind almost every plateau on thegranitic islands. They have virtually all been filled in or dislocated by piecemeal reclamation. The largestoccur on Praslin as well as about eighteen hectares on La Digue. Both have suffered from encroachment byagriculture, housing and roads in recent years.The coastal marine areas of the granitic islands can be systematically zoned into rocky shores orsandy beaches, rippled sand zone, marine grass beds, radial zone, algal ridge, reef edge, and outer slopes.The characteristics and the types of reefs have been described by various authors including Taylor, Lewis, Taylor and Lewis, Pillai et al, Stoddart, Littler and Littler. Fringing reefs are found at only a few parts ofthe coastline on the granitic islands and extend as uneven belts which may reach one thousand five hundredmeters in width on the North-western coasts of Mahe. The largest continuous fringing reef in the graniticislands stretching about twenty-seven kilometres on North East bay to Anse Marie Louise in Mahe has nowbeen interrupted by the East coast land reclamation and by the Seychelles International Airport. Sea grassbeds and the standing stock of algae especially Sargassum, are still very extensive and deserve particularattention especially as buffers of wave energy and erosion mitigating zones.4. COASTAL PROCESSES IMPACTING ON EROSIONPhysical coastal processes, which affect all coastalland forms,in Seychelles comprise:- Water movement;- Near shore water-borne sediment movement;- Aeolian transport ( wind blown sediment),particularly on some coral islandsThe reason for detailing these processes is to provide a basic understanding of them, and how theycan influence decisions on coastal change in Seychelles.Beaches and dunes are continuously affected by both wind and waves. Waves are generated by the

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 67effect of wind on the surface of the sea and, as waves approach the shore, they become steeper and then breakin the near shore zone. The interrelationship between wave height, wave steepness, wave period and thedirection of wave approach gives rise to the highly dynamic nature of a beach.Erosion ( the loss of beach sand) is usually caused by high, steep waves with relatively short periodswhilst accretion (beach sand build-up) is usually associated with lower waves and longer periods. Also,because waves often approach the shore at an oblique angle, long shore currents can be created.There is a continuous interchange of sand between dunes, beaches, sand bars in the surf zone andriver or estuary mouths. These 4 systems are known as the 'littoral active zone" and disturbing the naturalprocesses of any one of these could ultimately affect some, or all of the others.4.1 WATER MOVEMENTWaves are generated by wind stress and then propagated by the continual movement of waterparticles. The particles in successive waves do not actually move shoreward even though the wave itself ismoving. As a wave approaches the shore, the shallower water causes a shoaling process whereby the rollingshape changes to a steeper profile with a series of sharp crests and flat troughs and eventually the wave breaksShoaling starts when the water depth is half of the wave-length and the wave breaks once its height is about80 percent of the water depth.Wave refraction takes place when angled waves turn so as to approach the shore at right angles.Wave diffraction is the process whereby wave energy is transferred around an obstruction ( e.g. a breakwater)into the area behind.Long shore currents are caused by waves breaking at an oblique angle to the shoreline and occur inthe breaker zone . These currents generally move parallel to the shore, and are capable of transporting vastamounts of sand along the coast. The combination of the long shore current, together with waves "pushing"water into the surf zone can cause the formation of rip-currents ( the effect of a current surging outwardscounter to the in coming surf ) which are recognizable by a flattening of the breakers4.2 NEAR SHORE WATER-BORNE SEDIMENTBreaking waves stir up the bottom sediments thereby putting them into suspension and thesesediments can then be either moved onto the beach (onshore) or away from the beach (offshore) dependingon the wave characteristics. Sediments can also be moved parallel to the shore by a long shore ( littoral)current. In general, a beach will experience seasonal fluctuations of erosion and accretion but will still bein an overall state of dynamic equilibrium.4.3 AEOLINA TRANSPORTAeolian transport occurs when sufficiently strong winds blow over open, sandy areas, putting thesediment into motion . Most of this wind-blown sand is usually transported in a layer of up to 0.5 m abovethe beach or dune surface. The volume of wind-blown sand transported depends on various factors includingthe wind regime, dune vegetation cover and also sand moisture content, grain size and shape. It must be notedthat aeolian transport is more common on the coralline islands of the Seychelles than the granite ones.4.4 APPLICATION OF PHYSICAL COASTAL PROCESSESAn understanding of these processes is necessary in order to comprehend their effect on any coastaldevelopment or activity. The ongoing processes of water and sediment movement control the prospectivesiting of any development and, from these, a development "set-back" line can be determined ( this being thesafe seaward limit development, taking into account the dynamic equilibrium of accretion,erosion and aeolian sand transport).5. PROBLEM AREAS IN RELATION TO COASTLINE CHANGECoastline change in Seychelles may have various economic and ecological negative effects, such as:

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 68recession of beaches,losses of valuable arable or buildable landdamages to coastal property or infrastructures (buildings, roads, seawalls),destruction of economically valuable treesdestruction of ecologically valuable ecosystems or speciesCoastine change in the Seychelles is more often than not a natural process aggravated by humaninterference. Under the combined action of waves, tides, winds and currents, coastlines may experience aphenomenon of net advance and retreat. Alternate phases of beach erosion and replenishment are commonlyobserved, particularly on the northwestern coast of Mahe (Northolme Hotel beach). During stormy periods,beach material scoured away by the action of waves may be carried by current drift and deposited eitheroffshore, or onto another stretch of the coast (Pardiwalla's beach-Bel Ombre).Dunelands located behind the Seychelles beaches constitute a natural reservoir of sand for therestoration of the beach. In natural conditions, i.e. in the absence of hard structures such as roads, retainingwalls, etc... On the coastline, the increased erosional capacity of a storm surge would be accompanied by atransfer of material from the dune to the beach, thus flattening the beach profile and dissipating the waveenergy. At other periods of the year, when winds and currents have changed direction, the waves may carryagain some sand from offshore deposits onto the beach, which is thus replenished.Under natural conditions, most shorelines thus exist in a state of dynamic equilibrium, constantlyadjusting to changing environmental parameters. All beaches of an island or a group of islands participatetogether in this global equilibrium. However, various local factors such as a topography offering protectionfrom dominant winds, a flat sea-bed profile, the existence of a natural barrier such as a coral reef, thepresence of seagrass beds and marine algae cover may contribute to facilitate an early dissipation of waveenergy. This may explain why some sites are more significantly erosion-prone than others. This globalequilibrium is affected by man's activities, which may either obstruct the natural process of beach restoration,or even directly contribute to reinforce the eroding effect of waves.6. CLIMATE CHANGE AND SEA-LEVEL RISESeasonal fluctuations of beach profile are a normal feature in the context of the continuouslyadjusting coastlines equilibrium. However, there may exist a long term trend towards a net advance orrecession of the coasts, in relation to a general variation of the sea's level. This may in turn result either fromchanges in the volume of oceanic waters, or from slow subsidence or emergence of continental shelves.According to most predictions about 70% of all beaches in the world which have been the object of aregular monitoring over a long period of time, are actually receding. This phenomenon is primarily attributedto a rise in the sea level. It is recognized that the oceans would have been actually rising over the lasthundred years. This rise is estimated at 15 cm on average over the world, with important local variations.Substantial climatic changes have occurred in the Seychelles in the last one hundred years.Anomalous weather conditions have also been recorded recently by the Meteorological Services Division onMahe. According to a Seychellois expert, climatic anomalies such as "hypercanes" may become pronounced(Chang-Ko pers com). Increased incidence of storms, and high waves are anticipated. In 1986, a tide gaugeinstalled on Praslin for the TOGA Program was washed away by a storm! Rises in sea level would becatastrophic for the coastal zone, the newly reclaimed areas and the low coral islands; the majority of thepopulation and infrastructure would be affected. The worst scenario would be the simultaneous occurrenceof flash flood at high tide or worse still if there is a surge in sea level. It may be 15 to 30 years before seriousproblems occur, but current environmental damage, if not controlled, will exacerbate the effects of sea levelrise. It is unlikely that sea-defense protection offered by coral reefs will be much use beyond the year 2050.7. ANTHROPOGENIC EFFECTS AND SHORELINE CHANGESeychelles population of 68,600 is concentrated on the three largest granitic islands of Mahe(60,400), Praslin (5,600), and La Digue (1,900). Ninety percent of Mahe's population is concentrated on thecoastal strip, in particular the East and North Regions. With a total land area of one hundred and forty-eightsquare kilometres, the population density of the island is in excess of four hundred persons per square

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 69kilometres. This is comparable to densely populated countries such as the Netherlands and Switzerland. Inreality the density is much higher since almost the entire population is clustered in the lowland areas. Due tothe rugged and steep nature of the granitic islands and the favorable environment of the coastal zone, almajor touristic, fisheries and other economic activities are also centered in this area, competing for space.The coastal zone has therefore become the environmental "hot-spot" of the country.Various anthropogenic effects leading to shoreline change are given below:7.1 SAND EXTRACTIONAbstraction of sand for the construction industry, whether operated from the beach itself or from the"dry beach" or duneland directly contributes to the beach's recession. Mining of beaches for constructionmaterial can result in severe local coastal erosion because removing sand from a beach reduces the supplyavailable to renourish the beach. Likewise, the mining of sand dunes and plateau sand can affect sandreserves, and can lead to severe erosion problems and the recession of beach front among other environmentalproblems. The extraction of gravel from river beds can also induce erosion along the coast. It must beremembered that beach and plateau sand have traditionally been used as construction materials in Seychelles.Excessive extraction at the rate of thirty-five thousand tonnes a year from one beach on Mahe has beenknown. Since 1991, extraction of beach sand has been banned. Removal of sand blocking river mouths maybe permitted. Plateau sand is being removed in large quantities by permit. The replacement of this sand byimpermeable laterite soil in the plateau could lead to dangerous flooding and drainage problems. Alternativesto sand in construction, include crushed granite dust, pulverized coral fill (reclaimed material) and sand fromdunes on the outer islands.7.2 DESTRUCTION OF PROTECTIVE CORAL REEF SYSTEMS AND CORAL BARRIERSCoral reefs all around the main islands are under stress from multiple causes including terrestrial runoff,sewage, reclamation (mining), siltation, anchor damage, physical human impact and removal of livecoral. This is the least studied but an extremely important cause of coastal erosion in Seychelles. Expertsconsider the area from mangrove swamps and sandy beaches, marine grass and algal beds, to the outer reefedge as part of the entire contiguous reef system, which acts as a buffer against waves, currents and storms.Therefore, all these zones are interconnected, and the health of one will affect another.7.3 REMOVAL OF COASTAL VEGETATIONThe destruction of vegetation make remaining vegetation more vulnerable to abrasion by the windwhich blows sand inland (or seaward). Vegetation acts directly to reduce erosion by physically binding thesand to reduce turbulence. As stated earlier the main process by which coastal vegetation lost ground inSeychelles has been to make way for coconut plantations. Coastal vegetation is also removed for roads,playing fields, houses, hotels, fishing-related infrastructures etc. In addition, the Seychellois attitude of"netoye" or cleaning, sometimes results in removal of vegetation in the mistaken belief that by doing so theenvironment will be rendered cleaner and more hygienic.7.4 BUILDING ON SAND DUNESBuilding too close to the beach, on top of fore dunes or flattening them for construction sites limitsthe space available for the beach's natural erosion/deposition cycles. The construction of buildings orinfrastructures such as roads close to the shoreline therefore artificially isolates the beach from the landwardsection of its ecosystem. Wind blown sand is not retained anymore by the dune system and the beach, in turn,is deprived of its natural source of replenishment. This results in the undercutting of the buildings on thedunes, which then induces property owners to construct sea-walls, and in turn cause erosion problems. Thishas become a major problem with most coastal roads in the three main islands of Seychelles, since those havebeen built on sand dunes or the foreshore and now are locked in a never-ending cycle of construction andrepair of sea walls.7.5 CONSTRUCTION OF SEAWALLSThe construction of vertical hard structures like seawalls and revetments on the shoreline itself,hinders the dissipation of wave energy, reinforces their erosional capacity and thus causes accelerated beach

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 70erosion at the foot of the structure. The construction of these structures to protect property, road or as partof a small reclamation may accelerate erosion in front of and on the down drift side of these features becauseof wave reflection from the hard and often vertical surfaces. Usually, what has been experienced nSeychelles is that the fixed property (such as roads, houses, hotels) is saved for some time while the beachsand is lost. In the long term, it may often lead to the substitution of a sandy shore ecosystem by a rockiershore.7.6 CONSTRUCTION OF GROYNESUnless correctly designed and detailed, the construction of groynes will act as barriers to longshoredrift. The construction of groynes therefore , which aim at trapping sand carried by the drift current and thusfixing beach material in a definite place has the inconvenience of depriving down-drift beaches of their'normal' supply of sand. This artificial accretion of a particular beach is therefore usually achieved at theexpense of another beach. An example is at Anse Kerlans-Praslin Island (see page 10 of this report).7.7 CONSTRUCTION OF BREAKWATERS AND PIERSBreakwaters have been traditionally used for harbor protection, but have the side effect of starvingthe downndrift beaches of sand. The largest breakwater on Mahe is at Port Glaud and was constructed notas harbour protection but built by a hotel to "create" and protect a beach. It has led to severe loss of sanddowndrift. Continued deposition of sand between the shore and the breakwaters may eventually tie thebreakwater to the shore, thus affecting shipping. Continual dredging then becomes a necessity. This isevident at Bel Ombre on Mahe, where a breakwater constructed to provide safe anchorage for fisherman hasresulted in silting and a subsequent shallow lagoon which needs dredging. Piers, unless properly constructedlead to similar consequences as breakwaters as has been exemplified at La Digue Island.7.8 "IMPROVEMENT" OF BEACHESPrime quality tourist beaches (characterized by parameters such as fine sand, sheltered coves, goodbathing, no coral or marine debris, sandy sea bottoms and safety) are not common in Seychelles accordingto published reports, and in fact total only 5.6 Kilometres on Mahe, 3.5 Kilometres on Praslin and 1.7Kilometres on La Digue. There is therefore a tendency for some hotels to attempt to "improve" the beaches.One hotel built a massive breakwater to create a beach and artificial lagoon (see above), another cleared livecoral in front of the hotel and recently one on Praslin excavated tonnes of beach rock or sandstone.7.9 LAND RECLAMATIONLand reclamation projects on the East coast of Mahe near Victoria by dredging reef and calcareousmaterials started in the 1970's and have been completed in 1991/1992. The reclamation has led to siltationof reefs and destruction of live coral cover according to scientific surveys. Siltation of nearby reefs may bedue to land run-off as much as from dredging. In the final phase of the reclamation, silt screens and filtercloth were used to mitigate siltation, and filter cloth liner covered by rock armoring at the base of the fill areawas utilized to trap suspended solids.7.10 UPHILL EROSION AND DOWNSTREAM EFFECTSUphill soil erosion resulting primarily from deforestation has been documented as far back as the lastcentury. Run-off of Red Earth or laterite soils from cuts in the hillside is common during heavy rains andis a threat to reef systems. The advent of heavy earth- moving machinery and implementation of largeprojects has probably exacerbated the problem. In 1992 and 1993 road construction on hillsides adjoiningmajor touristic beaches resulted in large amounts of earth being washed onto the beaches and in the sea.The importance of human interference on coastal erosion is illustrated by the results of a surveyconducted at the end of 1987 in Mahe, Praslin, La Digue and Curieuse islands: Out of 40 coastal sites visited,the survey identified 11 sites where erosion was mainly due to natural causes, i.e. topography and marinehydrology factors while in 29 others, accidental erosion was mainly attributed to human activities andill-conceived development.

8. CURRENT ISSURS AND TOPICS IN SHORELINE CHANGE<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 718.1 BEACH SAND AS A RENEWABLE AND INEXHAUSTIBLE RESOURCESand from Seychelles beaches may be a renewable but is certainly not an inexhaustible resource.The Seychellois beach-system probably developed during the last 10,000 to 30,000 years from the action ofwaves, storms, calcareous algae and marine fauna such as parrot fish. The modern-day configuration andparameters took shape during the last 5000 to 6000 years. The replenishment rate is extremely slow. Sandabstraction above the replenishment rate will inevitably lead to erosion, recession and obliteration of thebeaches. This is unfortunately happening in Seychelles. many beaches are eroding and receding, somebeaches have already disappeared8.2 CAN SAND BE REMOVED FROM THE DUNES AND THE "DRY BEACH" WITHOUTADVERSE EFFECTS TO THE BEACH ?The dune lands and the "dry beach" form storm-water barriers and natural sand storage reservoirsfor natural beach repair. Removal of sand from this area will deplete the beach of repair material and leadto erosion & recession of the beaches.8.3 CAN SAND BE QUARRIED FROM ISOLATED BEACHES WITHOUT ANY ADVERSEEFFECTS ?All the island beaches form part of a total beach system "connected" by the coastal drift and aretherefore interdependent. Sacrificing whole beaches or partially abstracting from other beaches create"holes" in the total beach system. Other beaches will start eroding and the total sand-mass includingduneland and submersed storage will diminish leading to general erosion & recession of other beaches.8.4 MINING OR DREDGING OF SAND FROM SAND BANKS, BARS AND RIDGES IN THENEAR-SHORE ZONEThe sand banks, bars and ridges are formed from beach erosion during storms and are storagereservoirs for natural repair of the beaches. This is not surplus sand and it should be left alone. Howeversand may be mined or dredged from deposits in the ocean far enough away from the beaches and frommajor ecosystems, so as to not to disturb the total beach system.8.5 CONTINUING REMOVAL OF SAND FROM THE COASTAL TERRACESThe terraces or plateau as mentioned before took about 6000 years to be formed. At the present rateof abstraction, most of the available plateau sand on the main island might be exhausted within 25 years.8.6 CLEARING OF BLOCKED RIVER MOUTHS AND ABSTRACTION OF SANDClearing of blocked river mouths is necessary in order to ensure a steady drainage to the sea fromthe lower lying coastal plateau and marshes. This operation is normally performed by building contractors,concrete block makers etc., who are supposed to clear the river mouth itself of the blocking sand barrierand also clear the culverts under the coastal road. The contractors are allowed to abstract and take awaycleared sand. Unfortunately this operation contributes to the overall depletion of sand on the beaches. Ifpermanent sea-outfalls were installed through the sand barriers, very little contractor-assisted clearingwould be required, and much of the drainage problems on the coastal plateau would be solved as well.9. ATTEMPTED CONTROL MEASURES9.1 CONSTRUCTION OF GROYNES SO AS TO BRING BACK THE SAND AND RESTORE THEBEACH.Construction of groynes is a controversial matter. They are very costly and can do more harm than

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 72good. Groynes cannot re-create sand which has been lost through sand abstractions. In fact as has beennoted earlier, groynes can deprive down drift beaches of their normal supply of sand. In Seychellesespecially where the two biannually monsoon winds blow from diametrically opposite directions, theconstruction of groynes is a very tricky affair.9.2 CONTINUING CONSTRUCTION OF SEA WALLS TO PROTECT THE SHORE ANDSAFEGUARD INFRASTRUCTURESea Walls constructed on eroded beaches will initially protect the shore behind the seawalls, butin the long run sea walls and bulkheads have an adverse effect on the beaches themselves as mentionedpreviously.9.3 FENCING OF THE FORESHOREThe Division of Tourism has fenced certain areas on the foreshore where beach erosion has becomepronounced due to human and vehicular traffic. The fencing is with wooden bollards or stakes. In areas wherethis has been done successful regeneration of beach vegetation has been achieved10. CASE STUDIES OF SHORELINE CHANGE AND ATTEMPTED CONTROL MEASURES10.1 ANSE KERLAN/AMITIE-PRASLIN ISLAND.The beaches of Anse Kerlans and adjoining Amitie on Praslin Island are probably the mostspectacular example of shoreline recession in the granitic islands. The area has a narrow reef barrier whichoffers little protection. This reef seems to be under stress from anthropogenic causes, and this should beinvestigated more thoroughly (Shah pers obs.). The proximate cause of the beach receding is due to acombination of wave action and longshore drift. Simultaneously the southerly beach of Grand Anse havebeen enlarging due to accretion. This process is reputed to have taken place during the last 15 to 25 years.Apparently, a delicate balance previously existed between the two biannual littoral drifts: one in a generalnorth-westerly direction during the South East Trade Winds and the other in a general south-easterlydirection during the North west Monsoon. This balance has now become upset with the result that there is anet littoral drift in a south-easterly direction away from Anse Kerlans without a sufficient return of beachmaterial. The reasons for this are not clear, but it is thought that both natural and man-made causes play theirpart. It is the opinion of a professional coastal engineer that unwise development has disturbed the balance;developments on the beach and sand dunes include reclamations, houses, seawalls, roads, solid landing piers(Tilly, pers. com). As mentioned before, coral reef damage is also a factor that should be taken intoconsideration. There has been no attempt to monitor the beach profiles or the reef and therefore noquantitative data is available. Erosion is so severe that the coastal road has had to be divertedDuring the years, it has been attempted to protect the shoreline by construction of seawalls. Theseawalls have accelerated the erosion and the scouring of the sand due to increased wave reflection has ledto destruction of the seawalls. Rip-rap armoring of the backshore has also been attempted. Five groynes ofgranite blocks were constructed in December 1990 to provide protection to the shrinking coastline of AnseKerlans. It is clear from these that littoral drift traps sand during the North west monsoon and deprives downstream beaches such as Anse Korbiso (where there has been complaints of erosion) of its seasonalreplenishment. During the South East monsoon the action may reverse itself but at the expense of theadjacent Northern beaches. Erosion is still continuing at Anse Kerlans although the beach between thegroynes has stabilized.10.2 LA PASSE-LA DIGUE ISLANDErosion has become pronounced at La Passe where the port and landing pier of La Digue is located.The present day beach, to the South of the granite headland of Cap Barbu, comprises of carbonate and quartzsand mixed with coarser fragmented biogenic carbonate material from nearby dredging operations. This isbanked against an erosional scar up to 1 meter high in the older beach sands. The shore faces west-north-west.In 1991 a Fish Collection Center located on the backshore beach and the flattened dunelands in front of theyacht and schooner basin, was being endangered by shoreline erosion. The sea had undermined the landbeneath the Center and nearby coconut trees had been uprooted.

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 73Investigations showed that the "original" coastline had already receded by approximately 4.5 metresprior to the construction of the Fish Collection Center in early 1986. This was presumed to have been a resultof previous dredging operations in the yacht basin and destruction of protective reef platform and coral.Following more dredging operations in May 1990, further erosion of the beach speeded up with a recessionof approximately 5 metres. This left only 4 to 6 metres of flattened duneland behind the Fish CollectionCenterThe short term cause was identified by local experts as an open trench for a high tension electriccable dug between the shoreline and the Fish Collection Center which had not been backfilled and served asa conduit for backwash at high tide. However, the main problem is thought to be the existing pier which isa solid structure, except for two narrow culverts, acting as a groyne and trapping longshore drift sand. Theyacht basin therefore needs periodic dredging which is part of the cause of the beach erosion and shorelinerecession (Tilly, pers.com.). Arthurton, who visited the area on April 8, 1992, believes the recession maybe due to a net southward or south-westward drift caused by relative enhancement of the North-Eastmonsoon over the last 20 years or so (Arthurton 1992).Detailed recommendations by the senior engineer of the Ministry of Community Development andexperts from the Division of Environment have been provided for remedial action.. Nevertheless, a sea wallhas been constructed to protect the Fish Collection Center, contrary to the expert advice.10.3 BIRD ISLANDIn 1993 public attention was drawn to Bird Island, a coral island that lies on the Northern rim of theSeychelles Bank, as tourist chalets were undermined and destroyed by the encroaching sea. Bird is a flat sandcay with a height of 3.5 metres above sea level. The island has an area of only 0.56 sq. kilometres. It risesfrom a shoal depth of about 55 metres. The island is located to the windward edge of the shoal facing theSouth-Eastern trade winds. From east to south the island is framed by a narrow reef flat. There is no reefin the western side of the island facing the trade winds. The island is mostly composed of loose calcareoussand, although the interior previously was more solid being phosphate rock (all removed during guanomining operations). The island is a popular tourist resort and supports one of the largest colonies of SootyTerns (Sterna fuscata) a species of sea-bird, in the world. At present there is severe erosion of the southernwesternshore. Since there is no reef barrier protection in the western side, sand is being eroded from the westcoast, where the tourist complex is located. The island cannot expand to the east because of its proximity tothe edge of the bank and washing of material into the drop-off. There is a strong possibility, therefore, thatthe island may disappear altogether, especially if there is a slight rise in sea level.11. RECOMMENDATIONS THAT WOULD LEAD TO A NATIONAL POLICY ON COASTALEROSIONCoastal protection measures for Seychelles can meet the following objectives:To protect coastal property and infrastructure from distruction or inundation by the seaTo retain a usable beach for aesthetic or recreational purpose.Unfortunately, it is generally difficult to meet both objectives at the same time, since they frequentlyconflict with each other. As explained previously, in the natural process a beach is normally recharged bytransfer of sand from the duneland. On the other hand, the methods commonly used to safeguard coastalproperty, like seawalls, directly contribute to the loss of the beach. This is why the methods traditionally usedin the past to stabilize the coastal system with the use of artificial structures are today questioned by mostcoastal engineers and planners. Learning from the failure of several ill-conceived projects, engineers nowendeavor to formulate geomorphologically compatible measures and to make the maximum use of a varietyof natural defenses. This is usually achievable on the less developed coastline stretches.Where coastal development has gone so far as to prevent the coastline from reaching its naturalequilibrium, the natural choice for the decision makers would probably be to sacrifice either the beach, orsome valuable property or land. Neither of these are sustainable choices. In this context, it appears that asuitable coastal protection policy for the Seychelles should meet the following guide-lines :

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 7411.1 RESTRICTION ON SAND ABSTRACTIONSAll possible means should be investigated to reduce the consumption of sand by the constructionindustry, and to prevent any sand abstraction from beaches, duneland and coastal plateau areas. Abstractionof sand and gravel is regulated by the "Removal of Sand and Gravel" Act, 1982. A stricter enforcement ofthis act appears necessary to prevent illicit removal of beach and dune sand, which still exist. Achieving astricter control would require the following measures:To reinforce the means of the Environment Division to identify offenders.To involve more closely the police forces for the day to day control of abstraction or transportationactivities.To involve the District Councils in the enforcement and reporting of illegal abstraction.To impose on authorized license holders for sand abstraction the precise recording of all sales andtheir periodic notification to the Controller of Sand and Gravel. This would enable the establishmentof precise statistics on consumption, and facilitate cross-checks on the work sites to control the licitorigin of sand used by contractors.Besides the necessary strengthening of the legal control, the only permanent solution to prevent sandabstractions lies in a reduction of the demand, by way of adaptation of the construction technology.In that respect, two measures might contribute to signicantly reduce the consumption of sand by theconstruction industry.Production of granite crusher dust :The United Concrete Products company (UCPS) has put into operation a new crusher producing finegranite crush, which can substitute for natural sand in the manufacturing of concrete blocks andordinary masonry.Adequate measures, such as education, incentices and disincentives should be envisaged toencourage the use of this substitute material by the building contractors. In particular, the amount ofroyalties charged on the abstraction of natural sand must be raised, in order to create a disincentivefor its utilization. Such a measure would of course create additional grounds for reinforcingGovernment's control on illicit abstrations.Use of non-traditional materials for constructionThe use of prefabricated buildings and of non traditional materials such as gypsum boards forinternal walls must be encouraged, since fine coral sand is still apparently indispensable for the finalplastering of block work.11.2 PRESERVATION OF CORAL REEFSAmongst the various natural defenses which contribute to the protection of the coast, natural coralreef barriers are the most effective in dissipating wave energy and limiting their eroding effects. Existing reefsystems which include marine grass and algal beds as well as corals should therefore be protected from allpossible causes of deterioration such as pollution, excessive dredging, siltation etc.11.3 MANAGEMENT OF COASTAL AREA DEVELOPMENTEnforcing a strict control of development on coastal areas is a key element of any coastalprotection policy and for sustainable development. In the short term, such control is a precondition forsafeguarding and restoring coastal natural defenses such as vegetation-covered dunelands. It is also aprecondition to preventing the erection on the shoreline of hard structures which would disrupt theshoreline equilibrium and lead to accelerated erosion. In the long term, it is the only way to limit theeconomic losses which would be incurred by a rise of the sea level. In the context of such a threat, thewiser long term planning strategy would be to locate buildings and infrastructure on stable sites landwardof active coastlines, and to maintain wherever possible a coastal buffer zone free of costly development.Two practical measures can be proposed in order to improve the control of coastal development:Amendment of the Town and Country <strong>Planning</strong> ActSection 7(2)(b) of the Town and Coutry <strong>Planning</strong> Act stipulates that a planning permission is notrequired for "the carrying out by a hightway authority of any works required for the maintenance or

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 75improvement of a road". As a consequence, the upgrading of a coastral earthen track into a surfacedroad is not usually subject to planning authorization, although such works involving the erection ofhard structures along the shoreline may dramatically aggravate coastal erosion processes. As anillustration, the case recently occurred for the upgrading of Anse Kerlan road in Praslin. It isrecommended to amend sub-section of the Act.Creation of State-owned coastral land reserves or Domaine PublicIn the long run, the most effective way to ensure a strict control on coastral development whilstpreserving coastal environments, would be to constitute wherever possible stateowned coastal landreserves. On average, a state-owned coastal belt of 25 to 100 m in width, from the high-water mark,would seem reasonable, though the adequate width for such a reserve depends to a large extent ofthe coastal topography. Lorries and motor vehicles would be banned from entering this area and ofcourse no development would be allowed.11.4 CONSERVATION MEASURES ON UNDEVELOPED COASTAL AREASThe appropriate design of coastal protection measures requires a great deal of research and thought.However, as an interim measure, it is recommended to carry out simple conservative activities aiming atsafeguarding existing natural defenses in undeveloped, or little-developed coastal areas. Such activitieswould mainly consist in dune restoration and revegetation, protection of undermined coastal trees, relocationof access tracks, etc..11.5 PROPER DESIGN OF COASTAL PROTECTION STRUCTURESWherever the necessity to safeguard important coastal development does not leave any other optionthan building coastal protection structures such as sea-walls, bulk-heads etc., it is essential to minimize asfar as possible their negative impact. To that end, the determination of the appropriate location and designof such structures call for comprehensive preliminary investigations in order to ascertain the hydraulic andgeomorphologic parameters of the coastal system.11.6 EDUCATION AND INFORMATIONLegislation, government policy and good intentions do not guarantee that the shoreline will beprotected or utilized sustainably. Education and public information is vital for all the actors concerned tocomprehend the issues and factors involved in coastal erosion and shoreline change. A television programon this complex subject was produced locally in 1989 and broadcasted several times. A cartoon on the subjecthas also been made locally. However, consistent and factual information and education programs have notbeen attempted. The Division of Environment has had an Education and Information Unit since 1991 and itis hoped that this unit will become more active in this field.12. MANAGEMENT PLANS AND RESEARCH PROJECTS12.1 ENVIRONMENTAL MANAGEMENT PLAN AND OTHER REGIONAL PROJECTSThe Environmental Management Plan of Seychelles (EMPS) calls for CZM plans and studies andone study on sea level rise. They are the following:A.5 Impact Assessment of Climate Warming and Sea-Level RiseI.1 Coastal and Marine Environment Baseline StudyI.2 Beach Erosion ControlI.3 Alternatives to reduce sand in constructionI.4 Review of Coastal Zone Management PlansWith the exception of Project 1.3, none of these projects have been implemented. Projects I.1 andI.4 will be implemented shortly as part of a regional plan with financing from the EC under the auspices ofthe Indian Ocean Commission (COI). A national coordinator for the project has already been recruited.A major regional project namely EAF5, Coastal Zone Management <strong>Planning</strong> in the East AfricanRegion, under the auspices of FAO/<strong>IOC</strong>/<strong>UNEP</strong> has been recently implemented. The project for Seychelles

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 76will use the Beau Vallon area as a test case study. This area was agreed upon between FAO/<strong>IOC</strong>/<strong>UNEP</strong> andthe Division of Environment as a "hot spot" of coastal change.It is vital that a CZM Plan is formulated, implemented and followed very soon. In addition,education and training programs are an essential part of the process. Anthropogenic and man-made effectson shoreline change are mainly due to ignorance and lack of understanding even by high level policy makers.Very importantly, continuous and long term monitoring of erosion and of the marine environment needs tobe undertaken to provide time series data to base management decisions on.12.2 SEA LEVEL MONITORINGA sea level bench mark was established in the early sixties. Currently the prediction times andheights of high and low water for each day is prepared by the British Institute of Oceanographic Sciences.A tide gauge has been in operation in Victoria since the fifties. The predictions for Victoria is computed fromdata collected in the early sixties and astronomical parameters. At present, the Hydrographic Brigade of theSeychelles Coastguard, is responsible for collecting sea-level data and maintenance of the tide gauge.Analysis of the data is being undertaken at the University of Hawaii for the TOGA Program. An automatictide gauge which transmits real-time data to Hawaii has been installed in February of 1993.12.3 COLLECTION OF OCEANOGRAPHIC DATASince 1986, the French research and development agency ORSTOM has initiated computerizedoceanographic data bases for the Indian Ocean. The oceanic measurements collected by different institutionsfrom the beginning of the century have been gathered, validated and compiled into different formats. Thefour databases available are :Oceanographic Cruises MeasurementsVertical Profiles of sea temperatureSea surface conditionsRemote sensing satellite measurementsAlthough the databases were established for fisheries research and management, the applications areendless and can be used in monitoring environment and shoreline change.13. RELEVANT LEGISLATIONThere is no single piece of legislation which covers the management of the coastal zone. or coastalerosion. Various laws pertain to this area. A sound policy has evolved whereby considerable control isexercised in all aspects of development. <strong>Planning</strong> permission is required for all forms of development underthe Town and Country <strong>Planning</strong> Ordinance (cap. 160) and the Town and Country <strong>Planning</strong> Authorityregulates land utilization.The Land Reclamation Ordinance (chap. 152) and the Removal of Sand and Gravel Act (13 of 1982)requires licenses to be obtained before any operations can be commenced.Eleven areas have been set aside for nature conservancy under the National Parks and NatureConservancy Ordinance (chap. 1590 and public access has been limited in 24 areas under the Protected AreasAct (chap. 40). Other environmentally sensitive areas have traditionally been protected under the CrownLand and River Reserves Ordinance (chap. 150) and the Forest Reserves Ordinance (chap. 153).The protection, management and control of coastal trees is regulated by the Breadfruit and OtherTrees (Protection) Ordinance (chap. 122).The Beach Control Regulations (SI 77 of 1978) provides some protection for beaches. Damagecaused within the tourism sector can be probably managed under the Licenses (Accommodation, Cateringand Entertainment Establishment) Regulations (SI 16 of 1987).Maritime activities are regulated by the Harbour Ordinance, (chap. 210) and the Marine Pollution

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 77Regulations (SI 51 of 1981) which gives power to the Harbour Master to control discharges from ships.The Fisheries Act concerns not only fish but also covers the management of marine molluscreserves and the use of explosives on coral reefs and opening of navigational channels in reefs for fishermen.14. MANAGEMENT AND CONTROLThere is no overall authority for management of the coastal zone or coastal erosion. The Ministryof Community Development is in charge of land surveying and controls land and infrastructure development.Development of any land must go through a planning process as mentioned above. The Division ofEnvironment (formerly Department of Environment) of the Ministry of Environment, Economic <strong>Planning</strong> andExternal Relations manages some National Parks, one Reserve and all the forests. With the recent transferof authority of the Seychelles National Environment Commission (SNEC) to the Director of Conservationand National Parks, the Division of Environment is now the executive authority governing all protectedconservation areas in Seychelles.The Department of Tourism and Transport is responsible for tourism development, land and seatransport, and cleaning of beaches outside National Parks. The ports and Marine Services Division of thisDepartment is responsible for marine pollution and the Oil Spill Contingency Plan. The Meteorology Divisionof the same Department is responsible for monitoring climate change. The new District Councils areexpected to make by-laws which may have a positive impact on the management of shoreline change. TheSeychelles Fishing Authority is the central authority for all fisheries matters including coastal and marineacquaculture as well as collection of oceanographic data. The Island Development Corporation managesdevelopment on virtually all the outer islands.As in most countries, there is a confusion of roles and disputes occur. In addition, gray-areas suchas coral reefs and fresh water marshes present even day to day management problems. A huge constraintis the lack of technical personnel. Research, policy-making, management and administration are severelyhampered by this deficit in trained manpower. Mobilization of funds is another problem, in a small islandstate such as the Seychelles with a diminutive economy.ANNEX IList of Key National Experts (by Sector)Environment* Waldemar Tilly, Division of Environment, Ministry of Environment, External Relations and <strong>Planning</strong>(Expertise: Coastal engineering; coastal planning; erosion control; environmental assessment)Jean-Claude Michel, Division of Environment, Ministry of Environment, External Relations and <strong>Planning</strong>(Expertise: Town and Country <strong>Planning</strong>; National Parks and Protected Areas)Willy Andre, Division of Environment, Ministry of Environment, External Relations and <strong>Planning</strong>.(Expertise: Forestry; erosion control; marsh and estuary management)FisheriesEdwin Grandcourt, Research Section, Seychelles Fishing Authority. (Expertise: Fisheries research)HydrographyMichel Rosette, Hydrographique Brigade, Seychelles Coastguards. (Expertise: Hydrography)Lands and <strong>Planning</strong>Gerald Pragassen, Lands Section, Ministry of Community Development.(Expertise: Land and Surveys)Belinda Micock, <strong>Planning</strong> Section, Ministry of Community Development(Expertise: Town and Countryplanning)

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 78MeteorologyLuc Chang-Ko, Meteorology Section, Ministry of Tourism and Transport.(Expertise: Meteorology)Marc Desnouesse, Meteorology Section, Ministry of Tourism and Transport. (Expertise: Meteorology;GLOSS Engineer)Non Governmental Organization (NGO)Nirmal Jivan Shah, Environment.Resources.Oceans (ENVI.R.O) (Expertise: Coastal Zone Management;coastal and marine ecosystems; conservation and protected areas)TourismLindsay Chong Seng, Tourism Division, Ministry of Tourism and Transport.(Expertise: Beach control andmaintenance; conservation; natural history; botany)(All experts listed are Seychellois Nationals only, except for * who is a long time resident and the country'sforemost authority on the subject of coastal engineering and erosion control measures)ANNEX IIREFERENCESANONYMOUS, 1988. National Land Use Plan, Ministry of Community Development, Republic ofSeychelles.ARTHURTON, R.S. 1992 Beach erosion: Case studies on the East African Coast. Proceedings ofthe International Convention on Rational Use of the Coastal Zone. UNESCO-<strong>IOC</strong> ,Bordeaux 1992CHANG-KO, L.A. 1993 Vulnerability of the Seychelles Islands to Sea Level changes as a consequenceof GlobalWarminga n dResultingClimateChange.Manuscript.EasternHemisphere<strong>Workshop</strong> oft h eVulnerabilityAssessmentto Sea LevelRise andCoastal ZoneManagement. JapanGOVERNMENT OF SEYCHELLES. 1990. Environmental Management Plan of Seychelles1990 to 1995. Ministry of <strong>Planning</strong> and External Relations; Department of Evironment, Republic ofSeychelles.MARIEU, M. 1989. Hints about Coastal Erosion Phenomena and coastal Protection measures.Information Note. Manuscript.SHAH, N.J. 1991. Nature and Tourism in Seychelles. In: Tourism of Quality - A Concept of TourismDevelopment Compatible at the same time to Economic, Social and Environmental Aspects.AIEST Press, Switzerland.SHAH, N.J. 1993. The Coastal Zone of Seychelles. In Press.SHAH, N.J. and J.C. MICHEL. 1993. Oceanographic Processes and Sustainable Development inSeychelles. Submitted.SOCIETE CMPI. 1987. Etude sur l'erosion cotiere, Project Seychelles - 301/8704-14. Agence deCooperation, Culturelle et Technique REF/119/02. 1-82.

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 79TILLY, W. 1993. Seychelles National Report: Coastal Erosion and Siltation. Manuscript. <strong>UNEP</strong>(OCA/PAC) Regional Seas Program. Regional <strong>Workshop</strong>- December 1993.

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<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 86VI.NATIONAL REPORT ON THE STATUS OF COASTA LEROSION, SEA-LEVEL CHANGES AND THEIR IMPACTS ,TANZANIAN CASEby Y.W. Shaghude, M.K.D. Mutakyahwa , and Ms. Shufaa K.MohamedABSTRACTThe coastline development had been influenced naturally and artificially. The shoreline had been constantlyretreating since Jurassic time until Upper Tertiary times. Between Pleistocene and today it has beenencroaching the continent. The reasons for that are attributed to sea level rise. However, coastal erosion ingeneral has been observed to occur at different areas with varying intensity due to the fact that the causativefactors themselves vary along the coast. Mtwara, Mikindani, Kilwa, Dar es Salaam, Tanga and Zanzibarregions are cited examples of the most affected areas. The geometry of the coastline has been very muchmodified by wave actions which are controlled by bathymetry, to result into convergence or divergence waveswhich create bays and headlands respectively. Field observations have indicated that there are natural andanthropogenic factors which influence significantly the coastal erosion. Natural factors include geological(unconsolidated to semi consolidated sediments disturbed by tectonic movements), sea level rise, storm andwave actions. Anthropogenic activities include dynamite fishing, construction along the beach premises, sandand heavy mineral mining, mangrove cutting, coral limestone and beach rock blasting. It is suggested thatlegislative laws be closely followed, coordination between ministries, mass education on the question ofcoastal erosion and planting mangrove trees where they do not occur naturally be insisted.1. INTRODUCTIONCoastline changes or sea level fluctuations relative to the land is an ageless phenomena. Thevariationss can be worldwide or localised. It can also be a long lasting natural, geomorphic process or shortterm anthropogenic (man made) process. Long lasting geomorphic processes include isostatic adjustments,a process involving vertical movements of the land in response to an overlying load such as ice or sediments.Eustatic adjustments involve worldwide movements of sea level resulting from either the changes in the totalvolume of sea water, or the total volume of ocean basins. Usually the total volume of sea water decreasesduring glacial epochs. It is also believed that the total volume of ocean basins is affected by the rate of seafloor spreading. Fast rates of sea floor spreading increases the volume of the mid ocean ridges and hencereduce the total volume of ocean basins, the result is a high sea level. The opposite would be true for slowrate of sea floor spreading. Epeirogenic movements involve broad gentle up warping or down warping ofrelatively large crustal areas which may sometimes be associated with faulting.Coastline changes may also result from local human actions, which tend to interfere with naturalsedimentation processes or other processes which take at the interface between the ocean and land. Examplesof such activities include, removal of coastal natural vegetation such as mangroves, destruction of offshorebarriers such as coral reefs, offshore dredging, sand and gravel mining along streams which drain the beachesetc.The present report discusses the status of coastline changes in Tanzania. In particular, attention hasbeen made to review the current problem of coastal erosion in Tanzania (mainland as well as Zanzibarisland).Fieldwork done from the southern to the northern part of the territory include Mtwara, Lindi, Kilwa,Dar es Salaam, Tanga and Zanzibar regions. This has been done to assess the extent of erosion at the affectedsites. It can be generalized that there has been excessive erosion accentuated by sea level changes. Theseprocesses are supported by the disappearance of ancient towns, modern buildings and infrastructures.In order to acquaint the reader with the Tanzania coastal zone, attempt has been made to give ageneral view of the coastal environment of Tanzania. This is then followed by a discussion on the maintheme of the subject by citing specific examples of coastal segments where coastline changes have beendocumented. Our recommendations on what could be done to improve our future understandings of thecritical coastal segments which are being adversely affected by coastline changes are also suggested.

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 872. THE COASTAL ENVIRONMENT OF TANZANIA2.1 TECTONIC SETTINGSThe history of coastal geology of Tanzania can be traced back to Jurassic times. It is believed that,sometime during Jurassic, splitting between the continents of the eastern Gondwanaland (Australia, India,Madagascar and Antarctica) and western Gondwanaland (South America and Africa) took place along atransform fault parallel to the eastern coast of Africa (Le Pichon and Heitzler, 1968) and by Albian, that isabout 100 m.y. ago the opening between the eastern Gondwanaland and western Gondwanaland was complete(King, 1962).Following the opening of the Indian Ocean, full marine coastal environments developed along theeastern coast of Tanzania. The sedimentary column along the coast contain series of transgressive andregressive events which indicated that the shoreline had been moving relative to the present shoreline (Fig.1).Fault movements have at large controlled the coastal development. The topographic break betweenthe interior and the coastal plain is a geologic boundary marked by the sedimentary rocks of the coastal areaand metamorphic crystalline rocks of the interior plateau (Alexander, 1969; Kent, 1971). Faulting andwarping are also responsible for the formation of the three islands Pemba, Zanzibar and Mafia in the lateEocene (Kent, 1971) and for the formation of the coastal marine terraces discussed by Alexander (1968,1969).2.2 GEOLOGIC AND GEOGRAPHIC SETTINGSThe coastal belt of Tanzania consist of a narrow belt along the mainland coast as well as all the threeislands Pemba, Zanzibar and Mafia (Fig. 2). In the mainland as has been mentioned in section 2.2 thedistinction between the coastal belt and the interior plateau is based on rock formations. The coastal plateauis characterised by thick sedimentary rocks, varying in width between 17km at the Kenya boarder and 150kmin the vicinity of Dar es Salaam. The sediments which vary in age from Jurassic through Cretaceous toTertiary and Quaternary are composed of both marine and terrestrial sediments (Kapilima, 1984; Kent, 1971).The sediments are generally getting younger towards the east, and also dipping eastwards.The inland plateau on the other hand is characterised by metamorphic crystalline rocks of theMozambique belt, believed to have been formed during Pan African Episode, about 550+100 m.y. ago(Windley, 1977). The contact between the crystalline Precambrian basement and the coastal sedimentarybelt is sharp, and it is recognised as Tanga fault.The three islands Pemba, Zanzibar and Mafia resemble in many ways; they are all approximately 40km from the mainland, all aligned roughly in a north south trend, all composed of rocks ranging in age fromMiocene to Recent calcareous sediment with some marine clays, sandstones and coralline limestones, all arebelieved to be tilted and raised basement blocks whose size is comparable to other African fault blocks (Kentet al, 1971). The islands of Zanzibar and Pemba can be separated into three land forms:-(i)(ii)(iii)The channel country in Zanzibar and on the east coast of Pemba.The undulating and elevated to precipitous and Brocken Miocene rock.The flat coastal periphery or 'coral rag'country developed mainly in Zanzibar.It is believed that the presence of these islands has influenced the structure of the continental margin.Along the East African coast, the continental shelf is generally narrow except off Tanzania where it widensto include the three islands. The continental slope is 150Km east of Zanzibar.2.3 CLIMATIC SETTINGSThe entire coastal belt of Tanzania experience a tropical climate which is influenced by the monsoonwind system. The NE monsoons are often recognised during December to March, bringing short rains whilethe SE monsoons are recognised during June to September, bringing the long rains. The rains trigger the

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 88landslides in gullies which are followed by severe erosion. Associated with the winds are the ocean currents.The SE trade winds which blow with greater strength and constancy of direction is responsible for thenorthward moving long-shore current. It can obtain a velocity of 4 knots. The NE trade winds on the otherhand is weaker and only impedes the northward moving long-shore current but never reverses it.2.4 OTHER NATURAL SETTINGSThe coast of Tanzania is characterised by mangrove forests, fringing coral reefs, sweeping sandbeaches and rock outcrops (Kamukala, 1984). In the mainland mangroves are very common especially at themouths of both large rivers like Rufiji and other seasonal streams (fig. 3). Their total coverage along themainland coast is estimated to 79,937 hectares. Mangroves are also well represented along the coast ofZanzibar and Pemba (Fig.3), occupying a total area of 4,700 and 12,000 hectares respectively. Fringing coralreefs, sand beaches and rock outcrops occur elsewhere along the shore. Unlike the mangrove forests whichare well established at the mouths of rivers and other seasonal streams, fringing coral reefs are completelyabsent at the river mouths and other seasonal streams. This is due to the fact that high siltation takes placeat these areas and hinder their growth.3. THE PRESENT STATUS OF COASTLINE CHANGES IN TANZANIA3.1 PREVIOUS STUDIESThe earliest studies on the present status of coastline changes in Tanzania were conducted in 1960´s(Alexander, 1966,1969). Both Alexander (1966) and Alexander (1969) noted that shore erosion had beenactive along the Tanzania mainland from Tanga to Dar es salaam. On the basis of under rooted coconut trees,Alexander (1966) concluded that the present shore erosion along Tanzania mainland had been active at leastbefore early 1940´s.Alexander (1966, 1969) further observed that although erosion along the shore was discontinuous,it was still evident that the over all rate of erosion was increasing southward. Supporting this conclusion werethree pieces of evidence:(i)(ii)(iii)The shore zone mangrove stands indicated signs of increasing destruction south of Pangani thannorth of itThe incidence of under rooting of coconut trees (which are generally common all along the shore)through shore erosion was much greater in the south than in the northExposure of beach rocks through marine erosion was relatively common in the south than in thenorth.Alexander (1966, 1969) attributed the southward intensification of shore erosion to non- uniform rateof coastal uplift. He believed that the rate of coastal uplift was relatively higher in the north than in the south.After the work of Alexander (1966, 1969) many other workers documented the problem of coastal erosionalong different parts of the mainland coastline. Worth noting are the studies conducted at Maziwi island andDar es salaam area. These studies are the subject of the foregoing sections.3.2 MAZIWI ISLAND OFF PANGANI (TANGA)Fay (1992) discusses the history of Maziwi island (Fig.4). The island used to be locatedapproximately 50 km south of Tanga town and about 8 km southeast of the mouth of Pangani river. Accordingto Stuhmann (1894), the original shape of the island was roughly circular with a diameter of about 500-600m, corresponding to a terrestrial surface of 20-80 hectares. Fishermen interviewed by Fay (1992) reportedthat it took about 45 minutes to walk once around the island during colonial times. The island was originallyfamous for being the most important single nesting ground in East Africa for three endangered marine turtles(Olive ridley turtle, green turtle and hawksbill turtle), but has recently disappeared.Fay (1992) noted that this island was essentially composed of a shallow coral reef flat, reaching thesea level only during neap tides. On the western margin of the reef platform there is a sand spit composedof carbonate particles. He believes that the carbonate particles were derived from the coral reef flat anddeposited in a manner analogous to a submarine fan.

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 89Fishermen interviewed by Fay (1992) reported that between 1920´sand 1950´s there was nosignificant loss of the beaches belonging to Maziwi island, but the most significant loss of beaches is a recentphenomena which was first observed during 1960´s as evidenced by uprooting of casuarina trees. Fay (1992)reports that some zoologists eg. Shedd (1974) noted that by 1970´s the life of turtles was already under threat.The zoologists used to salvage the situation by transferring eggs of turtles that were laid below the beach crestto a safer place, further inland.According to Fay (1992), the last casuarina tree is believed to have fallen by 1977 and by 1978 theentire island was already submerged. Fay (1992) also discusses the possible causes of the disappearance ofthe island. He believes that direct interference of human with the ecosystem of Maziwi island can be ruledout as the main causal factor. Fay (1992) also rules out the possibility of the island disappearing due tosubsidence caused by crustal movements. Using the earthquake data between 1971-1986 he observed thatall of the earthquake epicentres were much too distant from Pangani (> 100 km) to cause any appreciablecrustal movement. Also he argued that the movement along the NNE trending Tanga fault which resultedinto the formation of the Pemba channel is of middle Jurassic age and there is no indication of anyreactivation of this fault during the Holocene. Also noting that the general trend of crustal movements alongthe East African coast since the Pleistocene has been positive as evidenced by raised Pleistocene coral reefterraces which occur almost every where in the coastal belt from Mozambique to Somalia, he concluded thatthe disappearance of the island cannot be attributed to tectonic causes.Fay (1992) also ruled out the possibility of disappearance of the island by erosion due toextraordinary heavy storm events. Interviewing four local fishermen, he was informed that the wind, currentor wave regime around Pangani have not changed, since they started fishing (1924, 1926, 1948, 1955). Allfishermen reported that erosion of Maziwi island beaches was most intensive during SE monsoon and thissituation came to be repeated more or less regularly on annual basis. On the other hand majority of thefishermen believed that the sea level today is higher than in former times and estimated a rise of 1 to 1.5 ft(30-45cm) since 1920´s. Fay (1992) believes sea level rise to be the main cause for the disappearance ofMaziwi island. He argued that although the rise of 1 to 1.5 ft since 1920 seem to be over estimated (since therise is relatively bigger when compared with the average eustatic rise of global relative sea level of 10 cmduring 1920 to 1980), Their estimation still conform with the globally observed trend. Fay (1992) arguedthat such a rise will inevitably affect the equilibrium of sand supply that may result into sand removal alongbeaches and will cause sand to be deposited further offshore. This will finally result into retreat of low-lyingcoastline composed of unconsolidated sediments by horizontal distance, hundreds to a few thousand timesthe amount of the vertical rise.3.3 COASTLINE CHANGES ALONG KUNDUCHI BEACH, NORTH OF DAR ES SALAAMPhysical settingKunduchi beach is located approximately 18km north of Dar es Salaam harbour. It has the form ofa gently protruding headland, treading roughly NW and stretching from Msasani Bay in the south and RasKiromoni in the north (Fig. 5). The beach is drained by five major streams, namely, Nyakasangwe, Tegeta,Mbezi, Mlalakuwa and Kijitonyama. The entire stretch of the coastline consist of a beautiful sand beaches,making it a nice recreational area. Because of this, five beach hotels have been built along the coastline. Thehotels are: Hotel Africana, Kunduchi beach Hotel, Silversand Hotel, Rungwe Oceanic Hotel and Bahari beachHotel. Other important buildings found adjacent to this coastline include, a Marine Biology building of theUniversity of Dar es Salaam and Fisheries Institute building. The beaches of the headland are erosionalformed in the old beach ridges with the frontal crest only 0.5-1.5m above HHW. The beaches are steep (10-013 ) and end rather abruptly on the bordering sands, almost level tidal flat, which has a mean width of 600mand a maximum width of 1,000m (NEMC, 1985).Literature reviewOutstanding documentation of beach erosion problems along this stretch of coastline appeared duringthe late 1970's and 1980's. Griffiths (1987) reports that members of the University of Dar es Salaam, beingaware of the problem formed an inter-disciplinary committee during 1977 and 1979 with the aim ofundertaking appropriate studies in the area (Schiller et al, 1977). Following these studies, several papers werepublished (eg. Schiller and Bryceson, 1978; Bryceson and Stoemer, 1980; Harvey et al, 1977, Mushala, 1978;Norman, 1985). For a better review of these studies, the reader is referred to Griffiths et al (1987).

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 90It is important to note that, some of the early papers reported erosion rate of up to 50m within a 10-year period (NEMC, 1985). Consequently some panic actions of beach protection measures were taken,mainly to protect the beach Hotels. The actions involved construction of 54 groynes north of Kunduchi-Manyema estuary. These were constructed within two year period from 1983. The groynes were constructedby loosely piled-up coral limestone boulders with an estimated average of 250-500kg, having an averagelength of 30m and height of 1.5m, a width of the base of 2m and the crest of 1m (NEMC). The spacingbetween groynes varied from 15 to 35m. Immediately south of Kunduchi-Manyema estuary where AfricanaHotel is situated, other types of groynes were constructed. These groynes were composed of sand filled withnylon textile woven tubes, with a diameter of at least 1m and average length of 70m. These were laid parallelto the beach and distributed with an interval of alternatively 60 and 120.All groynes were inspected on February 1985, and the inspection revealed that most groynes,especially those laid north of Kunduchi-Manyema estuary, were not built up high enough to cover the crestof the beach. They were also too short at the lower end, and the spacing was too close (Norman, 1985). Inview of this it became obvious that the groynes could not arrest the beach erosion problem. It was this stateof affair that the National Environment Management Council (NEMC), by then, an organ under the Ministryof Lands Housing and Urban Development, decided to form a committee, which thereafter became knownas the Beach Erosion Monitoring Committee (BEMC). BEMC was composed of members of different sciencedisciplines, most of them coming from the University of Dar es Salaam. The main objectives of thecommittee was to establish a comprehensive database from which to monitor the beach erosion problem inthe vicinity of Dar es Salaam (ie. Kunduchi beach). Thus, scientific data was collected in the followingaspects:(i)(ii)(iii)(iv)(v)Waves, current, tides and winds.Beach profiles.Aerial photographs and maps.Sedimentology.Sand extraction along stream beds.This data will be the subject of the foregoing discussion.The study of waves, current, tides and wind patternsThis study involved measurement of height and period of waves for the duration of one year, currenttracking using drogues, wind measurement using autographic anemometer and tidal recording at Dar esSalaam harbour. An account of this study is given by Lwiza (1987). Lwiza (1987) observed that erosionoccur during both SE and NE monsoon seasons, but it was more severe during the latter as the wave energywas higher. He believed that erosion was caused by a combination of high tides and big waves. He was ledto this conclusion after observing that daily Mean Sea Level could reach 20cm. Investigations of droguesshowed that there was a general tendency of being displaced offshore confirming a hypothesis put forwardby Norman (1985) that some sand was going offshore. Lwiza (1987) suggested that the sand is being erodefrom the beach by offshore drift and then moved and deposited offshore by tidal current.The study of beach profilesThe study of seasonal variation in beach profiles (configuration) is discussed by Hemed (1987), whotook fortnight measurements of beach profiles at seven different localities for a duration of one year.Investigations of the profiles revealed the following:(i)(ii)(iii)Large variations in the spot-levels were observable only on the first 40m of most profiles, so thatpoints further than 40m from the beach crest showed little or no variation at all. This suggested thatthere was nothing to be gained by extending the groynes across the tidal flat as apparently no erosionis taking place thereThe groynes built north of Kunduch-Manyema estuary were totally ineffective in stopping erosion;serving no useful purpose but only spoil the beauty of the beach, suggesting that they should eitherbe removed or rebuilt following proper specifications (fig.6). On the other hand the other type ofgroynes, south of Kunduchi-Manyema estuary, built at Africana Beach Hotel and their way ofalignment seemed effective as there was a net accretion on the profilesMsasani beach is least affected by erosion.

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 91Sedimentological studyA sedimentological study was conducted to analyze the ancient back shore sediment between BahariBeach and Mbezi Beach. The purpose of this study was to affirm the hypothesis that the Holocene sand thatis being erode from the shoreline between Ras Kiromoni and Mbezi beach is of marine origin (Fay, 1987).This would indicate that the intensive beach erosion affecting the study area is a recent phenomenon, probablyof anthropogenic cause (caused by man).In order to test the above hypothesis, attempt was made to collect samples by impact drilling along5 different traverses between Bahari beach and Mbezi beach (Fig. 7). Analyses of the core samples indicatedfrequent occurrence of charcoal pieces, giving an evidence of sand accretion along this part of the coastduring historic times and up to perhaps few decades ago. It was also apparent that the uppermost layers ofthe youngest beach ridge contained heavy mineral concentrates, indicating a low sand supply at present incontrast to the high sand supply of the former times.Sand extraction along stream beds and the study of Aerial photographs and mapsFrom the study of Fay (1987), it was apparent that the amount of sand supply on the present beachesof the study area was significantly low. Also, analysis of Aerial photographs and maps showed that themorphology of beach ridges and sand spits suggested that longshore drift has always been towards the northand has been a long continuing process (Griffiths, 1987). In view of this it was therefore clear that somethingelse must have changed to influence the low sand supply at the beaches.Griffiths (1987) noted that there has been a drastic change in land use such that natural vegetationhas been largely replaced by cultivation, secondary bush or buildings. However, removal of naturalvegetation leads to greater surface run-off and increased sediment load in rivers, and if this were the onlychange, one would expect the supply of sand and silt to the beaches to have increased and not decreased.Hence the dramatic change in land use cannot explain the current observed decrease in sand supply on thebeaches. Griffiths (1987) observed that there has been a dramatic boom in building constructions in Dar esSalaam since the beginning of the 1980's. The present authors examined aerial photographs between 1970and 1993 and noted the same thing. It is clearly evident that a such a dramatic boom in building constructionsgoes hand in hand with a great demand for building materials namely, sand for the manufacture of concreteblocks. In Dar es Salaam, the majority of people who build concrete blocks obtain there sand requirementby buying lorry loads of sands which other people have dug from local stream beds. Griffiths (1987) reportsthat sand digging from stream beds around Dar es Salaam is a big business which employ many youths,especially ex-standard seven.Bryceson (1980) put forward the hypothesis that sand extraction in the Tegeta stream with thedestabilization of the beach crest in the vicinity of the Heavy Mineral Plant (which used located at Silversandin the Mid 1970's) accelerated the erosion to the north. Griffiths (1987) examined the aerial photographsalong the mouth of Tegeta to affirm Bryceson's hypothesis. Examination of the photographs between 1960'sand 1980's revealed two contrasting situations (fig.8); the latter photographs showing a progressive evidenceof disturbance. A field survey was conducted by Griffiths (1987) to estimate the extent of sand extractionalong the four main streams (Tegeta,Mbezi, Mlalakuwa and Kijitonyama) which drain the hinterland ofKunduchi beach. The survey involved among other things:(i) Walking along each stream bed to estimate its length, width and depth of sand extraction. Thisinformation was subsequently used to calculate the annual volume of sand for each stream(ii) Count the daily number of lorry loads coming from the sand extraction sites of the above streams.The average daily counts was multiplied by 300 to obtain the annual estimate of sand extraction.It is interesting to note that the annual estimates obtained by both methods were more or less similar3(Table 1). Griffiths (1987) found that a minimum of 100,000m of sand was extracted annually from the fourdisturbed streams that drain the hinterland of Kunduchi beach. She concluded that, if the sand extracted from3rivers equalled the deficit on the beach, then 100,000m /year would be equivalent to a retreat of 10m to adepth of 1m along a length of 10km of coastline; which is approximately that distance suffering severeerosion between Mbezi beach and Ras Kiromoni.Table 1: Annual volume of sand extracted along variousstream beds draining Kunduchi beach.

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 92Name of stream segment of stream Estimated vol. of sand (m )Method 1 Method 2___________________________________________________________________________________Between the bridgeon the old Bagamoyo 12,000 13,446TEGETAroad and the streammouthBetween the bridgeson the old and new 5,000 -Bagamoyo roadsUpstream of the bridgeof New Bagamoyo 48,000 65,000to Telegraph lineMBEZIBetween bridges onthe old and new 37,000 33,615Bagamoyo roadsUpstream of thebridge of New 150 -Bagamoyo roadMLALAKUWABetween military campand University 32 -perimeterWithin Universitypremises - 936Downstream from thebridge and outside 2,000University premisesKIJITO- NYAMA - 5,603Other important studiesOne important conclusion which draws from the studies conducted by the Beach Erosion MonitoringCommettee is the affirmation that the ongoing beach erosion at Kunduchi beach area has by far beenaccelerated by certain human activities conducted in the hinterland. Bryceson (1978) and Mushala (1978)had earlier observed other human activities conducted offshore which had similar effects on the coastline.In the offshore zone of the study area there are three islands (fig. 9), namely, Bongoyo, Pangaviniand Mbudya. The islands are believed to be uplifted coral reef platforms (Alexander, 1968). These islandsare surrounded by vast active coral flats. In addition to these three islands there are two other relativelysmaller coral reef platforms, namely Mkadya and fungu Yasin and several more submarine ridges.Bryceson (1978) and Mushala (1978) reported that the reefs were in great danger of being destroyedby dynamite fishing. Since these natural structures protect the shore from wave attack, Mushala (1978)believed that their destruction would ultimately intensify the coastal erosion.4. COASTAL EROSION IN ZANZIBARZanzibar consist of main Islands (Unguja and Pemba) with a number of islets doted almost all alongtheir costs. Most of these islets are found on the Western side of the island. The islets, around the islands areof Pleistocene corals. Very beautiful extensive corals can be found around some of these islets and reefs, for

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 93example Mnemba, an island North East of Unguja, Misali island South East of Pemba, Nyange reef andMurogo, near Zanzibar town etc. A continuous fringing reef, a high energy reef with a back reef /lagoonsystem which dries up at low water, runs along the length of the island, from Ras Nungwi to Ras Kizimkazi.This, together with the islets, the mangrove habitats found in areas like, Kisakasaka, Chwaka, Bumbwini andparts of Zanzibar town form natural barriers against the strong waves and current, around Zanzibar.Zanzibar island is generally flat. Due to lack of positive relief features, there are no rivers. There areonly few streams, most of which dry up during the dry season. One can therefore see that hinterland sandresource is very scarce. The current population of Zanzibar, according to the 1988 census is about 640,578people with 314,864 males and 325,714 female. The average household is 4.6 with an annual growth rateof 2.9% and a fertility rate of 8.24. In the urban areas such as Zanzibar town, Chake, Mkoani and Wete, thegrowth rate is much higher than the above quoted figures. The same is true for the overall coastal strip. Sincethe coastal strip is not expanding in response to population growth, one should expect to find intensificationof coastal activities and an overall continuous degradation of the coastal environment and significant loss ofbeaches. This is indeed what has been, and is still happening.Coastal activities which are believed to create negative impacts on the coastal environment includefishing, beach sand mining, quarrying along coral rag areas and mangrove cuttings. The foregoing sectionswill elaborate how these activities degrade Zanzibar coast.4.1 FISHINGAs stated above, the island is encircled with a number of islets most of which are made up of corals.The islets therefore offer the coast a natural protection against strong wave actions, which normally erodethe beaches. A number of bad fishing practices are occassionally practiced although they are not allowedlegally. The bad fishing practices include dynamite fishing, 'Kojani' fishing etc.. Apart from bad fishingpractices, careless anchorage of the vessels and pollution outfalls from the urban areas and industries alcontinuously degrade the coral habitats.4.2 BEACH SAND MINING AND QUARRYINGThe island of Zanzibar is mostly covered with coral rags, with only minor sand patches in thehinterland. Due to lack of sand in the hinterland both the governmental sectors and local people frequenly usebeach sand and sometimes coastal limestone quarries for building requirements and road constructions.4.3 MANGROVE CUTTINGSMangrove ecosystem trap sediment and maintain coastal water quality. Mangrove coverage alongthe coast of Unguja island is estimated to 4,700 hectares. It is of interest to note that the entire mangrovehabitat has been declared as reserves. However, cutting for daily local uses such as fuel, building poles etc.is allowed. Cutting for selling is only allowed on selected areas. Not all mangrove users adhere to theseregulations. Once in a while it is common to observe destructive cuttings.4.4 MAGNITUDE OF EROSIONIn order to visualise the magnitude of erosion experienced in Zanzibar, two localities, Nungwi andMaruhubi, which are believed to among the worst affected have been taken for elaboration.Ras NungwiRas Nungwi is at the North tip of Unguja. The area is of coralline and reef lime stone with theexceptional of a small area which is top covered with sand. Due to the poor soil formation, Nungwi is poorlyvegetated with coral rag thickets. A number of casuarina trees are found along the beach. A salt lake, withits depth changing according to tidal movement, is at the Eastern side of Ras Nungwi. There are other patchesof salted areas with very weak mangrove habitat.The areal photographs shows an increase in population growth from almost zero 1947 to a highlydensity area in 1989. Due to lack of mangrove poles, Nungwi houses are normally of stone and masonry.Sand used in the masonry is from the sea shore. Other activities on the sea shore are boat building, which

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 94involve general boat building, launching and repair.The coral cover of Nungwi is poor, 15 to 30% [<strong>UNEP</strong>, 1989] and those colonies present wereencrusting on a scoured Pleistocene coral substrate. The fore reef had been extensively colonised by softcoral species. There is heavy pressure on the area by local villagers who literal swam onto the back reef insearch of octopus and mollusc species [<strong>UNEP</strong>, 1989].Waves at Nungwi are wind driven, and they are believed to be the main cause of erosion. The arealphotographs shows the erosion of the area to be very high, suggesting an average rate of erosion of 3m/yearbetween 1947 and 1977, and 4.5m/year between 1977 and 1989. The increase in the latter is thought to havebeen caused by the collapse of the sea retaining wall in 1984. This wall was a very weak structure and wasbuild in an attempt to protect the area, but lasted only for one year.The study made by the Institute of Marine Sciences, stated that, no definite single cause is responsiblefor erosion; sea level rise, destruction and low growth of corals and sand beach mining are the majorcontributor to the problem.MaruhubiMaruhubi is at the Western side of Zanzibar Island. It is in the vicinity of Zanzibar town. To theNorth is bounded by Beit el Ras and to the South by the Malindi spit. The area accommodates three seasonalstreams and a tidal flat, with a tidal range of 4m. The study was based on the existing knowledge on EastAfrican waters, admiralty charts and wind data. With basic interest on the relationship between coastalerosion and long-shore drift, geology and of the coastal rocks, wind generated sea waves and geomorphologyof the area. This was done during the months December to March, the most active months with regard to landrecession by erosion.Geology and GeomorphologyThe beach is of sands which are in a continuous process of erosion and deposition. Sand istransported from Malindi spit area during S.E monsoon and the another possible source of sediment is thePepo stream neighbouring the restaurant on the north. Adjqcent to the berm of the beach is a terrain ofunconsolidated raised beach sands [Nyandwi, 1986]. These sands are quite unstable against wave erosion.The important geomorphological features include the coral islands of Zanzibar town and streamindentions. The islands protect the beach from the wind generated waves. At the mouth of the stream a groupof mangrove existed. Their disappearance is thought to have been caused by the pollution coming fromindustries which are discharging their effluent in this stream. The stream mouth, which is of 'V' shaped, isinvaded by the tidal current and when the current coincide with strong waves they erode the channel walls.Beach ErosionErosion at Maruhubi is a threat to the Maruhubi restaurant. Due to the high rate of erosion therestaurant management built a wall to protect their property. However, this wall failed to stand the strongwaves battering it. Examination of admiralty charts indicates an amount of > 3m a year [Nyandwi, 1986].Wave battering increase during high tide and N.E monsoon period. The action takes away any available sandin front of the wall as a backwash, and hence no deposition is affective at the site [Nyandwi, 1986].Underground seeping under the wall increase the problem and weaken the sea wall farther. It was observedthat long-shore sediment transport from the north was interfered by the break water, built perpendicular tothe beach neighbouring the river, constructed to hold back the waves in order to accommodate thetransportation of road construction equipment, during 1979.The total course can be summarised to have been due to net Northward long-shore sediment transportdeposits.5. SUMMARY, DISCUSSION AND CONCLUSIONS5.1 OBVIOUS RECOGNITION OF COASTAL EROSION(i)Dar es Salaam - Ras Kiromoni, Msasani Bay and other areas along the coast like Silver sands, Bahari

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 95(ii)(iii)(iv)(v)(vi)(vii)(viii)(ix)Beach, Oysterbay and Kunduchi Beach Hotels are being threatened by erosion.Bagamoyo shoreline is as well being threatened by the same effect and so is the Ocean Road a partof Dar es Salaam City.At Kilwa Kivinje the wall built by Germans to protect the houses nearby has been broken down byoceanic waves and some of the houses have been eroded.At Kilwa Kisiwani some of the ancient buildings and an ancient cemetry have been eroded. Theerosion of the ancient cemetry has left some exposed skeletons. The foundations of the Great Towerat Songo Mnara has been affected as well.The disappearance of ancient towns like Kaole and Maziwi Island and archaeological sites is dueto excessive coastal erosion. This leads to the disappearance of important archaelogical information.ODADA, 1993 sees that also the sea level rise is the main cause of erosion in most parts of easternAfrica Coastline.Mikindani town a part of Mtwara is constantly being eroded. This results in destruction of ancienthouses and productive land. A part of the railway line is currently about 10 m in the sea.At Lindi, most of the houses at the beach have been eroded including the present Beach Hotel. Theplace is being undercut by the oceanic waves.In Zanzibar, Maruhubi, Nungwi and Paje are the most affected areas where the rate of beach erosionis estimated to be more than 3m per year.Cutting of the mangrove trees for making salt pans along the coastal area.5.2. REASONS FOR COASTAL EROSION IN TANZANIA(i)(ii)(iii)(iv)Dynamite fishing - this type of fishing is illegal according to national legislations. It destroys thefishing beds and the coral reefs which protect the coast against the oceanic waves. The coral reefsare barriers and once they are destroyed, wave energy is intensified thus causing major erosion alongthe coast.In some areas like Mtwara and Mikindani quarrying of beach rocks and coral limestone for houseconstruction is common. In Zanzibar coral limestone is mined for lime making.Sand mining from the inland rivers and streams limits the amount of sands from reaching the coast;heavy mineral mining from the beach distabilize the beach.Construction of buildings and cultivation along the coast. The on going construction of hotels nearthe beach must discouraged.(v) Geological influence - Tanzania coastal sedimentary belt is constituted by unconsolidated to semi -consolidated sediments; and hard coral limestone and sandstones. The former are very succeptibleto erosion. Landslides followed by gully erosion start along tectonic linearments (faults and streams).(vi)(vii)(ix)A natural process which is geological is the rising of the sea level. Its effect can be recognized aftera long period. However small change in sea level may induce significant coastal erosion.Blasting of hard rocks e.g. limestones at Wazo Hill, Dar es Salaam for industrial purposes create landinstability leading to landslides.Parking of cars along the beach premises.5.3 MEASURES TAKEN(i)(ii)Groynes have been constructed using coralline limestone blocks and piping along Silver Sands,Bahari Beach and Rungwe Oceanic Hotels. This is not done for the entire coastal line. It has beenpointed out by the Glasgow University - Tanzania expedition 1991, that groynes do not stop erosionbut increasingly interfere with sand transportation.Concrete sea walls along Ocean Road in Dar es Salaam, near Zanzibar Harbour. The old sea wallbuilt by Germans at Kilwa Kivinje has been broken down by oceanic wave action. Sea walls haveto be constructed and maintained regularly.5.4 NATIONAL LEGISLATION ON COASTAL EROSIONIn Tanzania mainland, all mining activities are vested upon the Ministry of Water Energy andMinerals. The legislations which govern the extraction of minerals including heavy minerals, mineral sandand gravel are defined in the mining Act of 1979 and the subsidiary legislation on Mining regulations of 1980.According to these Regulations, all prospectors who wish to extract coastal sand are required to submit formalapplications to the City Council and prospecting Licence from the Ministry of Water Energy and Mineralsto obtain permission to prospect for sand in a specified area. After getting permission, the applicant is

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 96required to peg the Claim by erecting temporary markers at one corner of the Claim indicating its dimensionand bearings together with posts or cairns of stones at the remaining corners. The applicant's claim is thenentered in the Temporary Register of Mines. After getting permission from the City Council the applicant isrequired to apply to the Regional Mines office for a prospecting license. The Regional Mines Officerscrutinize the application and if the application is approved the Claim is entered in the Rent Register ClaimLedger. The ledger contain among other things, the information on the length of time specific lease havebeen held.Griffiths (1987) analyzed both the Temporary Register of Mines and the Rent Claim ledgers, onlyto find that there were very few claims in spite of the fact that a lot of sand extraction had taken place overthe years. This was an indication that most of the sand extraction was taking place illegally in front of thegovernments' eyes. She noted that attempt to stop the illegal sand extraction activities by the Ministry ofLands, Housing and Urban development had been made several times but with very little success. Griffithsbelieved that one of the reasons why it was difficult to stop illegal sand extraction activities was because theactivities were already becoming big money earning ventures for contractors, lorry owners and the sanddiggers. She reports that most of the sand diggers were young youths and ex-primary school students, fromthe surrounding villages.In the case of Zanzibar attempts are being made by the responsible Departments (Department ofEnvironment and Department of Fisheries) to minimize activities like improper sand mining, coral destructionand mangrove cutting.The problem of coastal sand mining in Zanzibar, is similar to what has been discussed for themainland. In particular, all prospectors who wish to mine sand are required to apply for legal permits beforethey start mining sand in the selected areas. However, most people do not go for these permits. Instead, theydo not only mine in the selected areas, without permits, but they even mine along the beaches and otherrestricted areas.Concerning the coral destruction, one approach which has been used is "Community ManagementProgram". This is a program which have been started in a number of villages southwest of the island ofUnguja, involving the control of destructive fishing methods and over fishing by the local villagers. Theselection of southwest Zanzibar for this program was basically done on the fact that this part of Zanzibar hasmore fishermen than other parts of Zanzibar. Elsewhere in Zanzibar, traditional protecting methods are used.These involve the closing and opening of fishing periods. The closing normally is only for a certain type(s)of fish. Village leaders carry the responsibility.Another measure which is being taken is to discourage coral and shell for tourist market. In 1950-1970's shell export trade was very common. It is known that the main collection was coming from Nungwi.No permits are issued for this kind of trade at present.Collection of corals for lime, is a well known business in many parts of the islands. In Pemba for instance,people collect coral stones from the Kwata island for TSh.400/=, a cart. Given the availability of rocks onland, it is unnecessary, though in some areas coral lime is preferred. However, there is no study done toinvestigate the extent of annual collections.Fisheries (general) law covers the destructive fishing methods under section 14.1 and 25.25. ''Any person who contravenes any of the provisions of section 14(1) shall be guilty of an offence and shallbe liable on conviction by a court to a fine not exceeding ..... Shillings''.Section 14.1 of this legislation forbid the use of destructive fishing methods like, Kojani, poisoning anddynamite fishing. There is no law covering collection of corals at the moment, but this issue is covered in theEnvironmental Policy. An environmental legislation is in preliminary preparation.The first attempt to managing the mangrove resources started in the 1940's. It is interesting to notethat, by then mangroves were managed not for beach protection purposes but just as an ecological resource.In 1945, mangrove areas were declared as Government land (under wood cutting Decree N.18). The Decreeprovides for controlled issue of cutting permits. In the year 1959 certain mangrove areas were declared asreserves. By 1965 all Mangrove forest were gazetted as reserves (L.N 92 of 1965) and they are under directresponsibility of Commission for Natural Resources at the moment.In view of the above it seems that in order to effectively succeed in banning the illegal sand

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 97extraction activities, the following issues need to be given some further attention:(i)(ii)(iii)(iv)Youth employmentMass educationAlternative source of sandCreation of a buffer zoneIt is quite interesting to note that employment opportunities particularly in the urban areas like Dares Salaam is not keeping pace with the fast increasing number of youths completing primary schooleducation. This trend inevitably goes hand in hand with the increase of criminal cases as most of the youthfind no alternatives, but earning their living requirements by doing illegal activities such as unlicensed sandmining and even robbing! Therefore it is high time that the Governments policy should critically address thepresent unemployment crisis.The question of mass education is also of vital importance especially in the situation like the presentone where the people themselves are required to assist in enforcing the law. However, the people would noteffectively enforce any law unless they are carefully educated on the 'overall gains' of the law. In the presentcase, the people should be educated on the importance of preserving our coastal environments, and howcertain human actions could adversely affect the coastal environments. Mass education could be achievedthrough Radio and/or Television programs, Newspapers and Education curriculums. Although one may notsee the immediate outcomes of such measures, the long term outcomes are quite certain.Also, the government need to identify other suitable sources of sand resource. Suitable in the sensethat, it is technically of good quality and at the same time environmentally safe. Such areas should besurveyed by skilled geologists to determine the amount of sand resource present and this data should be usedby land use planners.Finally, the authors strongly support the suggestion put forward by BEMC of setting a buffer zonealong the cost. The buffer zone would serve the following purposes:-(1) It would decrease the intensity of human activities in the coastal zone.(2) The natural vegetation present in the buffer zone would help to stabilize the beach.BEMC had earlier recommended a 200m for the mainland. However, due to conflict of interestsbetween different users of the coastal zone, it had been difficult to implement the suggestion. RecentlyNEMC had proposed a 60m buffer zone. Zanzibar case is a bit different; setting for instance of a 60m bufferzone would imply a significant loss of useful land. A suggestion of 30m buffer zone has been made instead.The suggestions of setting buffer zones in both the mainland and Zanzibar has been accepted in principle bythe departments (or Ministries) concerned.5.5 ESTABLISHMENT OF COASTAL INVENTORYThe present authors are of the opinion that, the problem of coastal erosion in Tanzania is not yet fullunderstood. In particular, the information concerning areas which are critically being affected by coastalerosion have only been gathered or documented in few areas of the coastline.In view of the above it is suggested that attempt be made to establish a coastal inventory for the entirecoastline (including the main islands Pemba, Zanzibar and Mafia). An inventory of this type may containamong other things (Fay, 1992), the modern classification of the coast following the guidelines discussed byQuelennec & Ibe (1989). This can be achieved by analysis of aerial photographs and maps, accompanied byground control methods. The results of such studies could then be used to identify coastal segments whichare critically endangered by coastal erosion. Once such segments are identified they form a base for advisingthe government regarding future coastal plans and coastal protection measures. Thus, continuous monitoringof shore processes and prompt decisions on appropriate beach defense measures are the key elements forfighting coastal erosion.5.6. OTHER RECOMMENDATIONSMangrove plantations along the coast may help to break the wave energy and thus protect the coast

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 98from erosion. They also interfere with sediment transport along the beaches. These trees are usually naturalbut they can as well be artifially planted.ANNEX IREFERENCESALEXANDER, C.S. (1966): A method of descriptive shore classification and mapping as applied to thenorth east coast of Tanganyika. Annals of the assoc. Am. Geographers, 56(1), 122-140, NewYork.ALEXANDER, C.S. (1968): The marine terrraces of the north east coast of Tanganyika. Zeitschrift furGeomorphologie, Bd7, 133-154, Berlin, Stuttgart.ALEXANDER, C.S. (1969): Beach ridges in the north eastern Tanzania. Geographical review, 59(1), 104-122, New York.BRYCESON, I. (1980): Silversands Hotel beach erosion control. Int. memo to University of Dar essalaam, 2p.BRYCESON, I. and STOERMER, K.P. (1980): Recommendation for beach erosion control at SilversandsHotel. Rep. to University of Dar es salaam., 20p.COLBERT, GEORGE, WAGNER, BERNHARD, H. and PINTHER, MICKLOS: Hydrological Map ofZanzibar. Cartographic Unit, United Nations Department of Technical Cooperation forDevelopment Executed Project URT/80/001.FAY, M.B. (1987): Ancient backshore sediments between Bahari beach and Mbezi. In "Beach ErosionAlong Kunduchi Beach, North of Dar es salaam." Report for National Environment ManagementCouncil by Beach Erosion Monitoring Commettee. pp. 32-35.FAY, M.B. (1992): Maziwi island off Pangani (Tanzania): History of its destruction and possible causes.43p., <strong>UNEP</strong> Regional seas Reports and Studies No. 139. <strong>UNEP</strong> 1992.GLASGOW UNIVERSITY - Tanzania Expedition Report (1991): Study of coastal erosion along IndianOcean Coast in Dar es Salaam Region. Report IRA, Dar es Salaam.GRIFFITHS, C.J. (1986): The Geological evolution of Tanzania. Jour. Geog. Ass. Tz., 24, 1-25.gCommittee. pp. 48-53.GRIFFITHS, C.J. (1987): The impact of sand extraction from seasonal streams on erosion of Kunduchi.In "Beach Erosion Along Kunduchi Beach, North of Dar es salaam." Report for NationalEnvironment Management Council by Beach Erosion Monitoring Commettee. pp. 36-47GRIFFITHS, C.J. (1987): Conclusions and Recommendations. In "Beach Erosion Along KunduchiBeach, North of Dar es salaam." Report for National Environment Management Council by BeachErosion Monitoring Commettee. pp.48-53.HARVEY, J.G. and DUYVERMANN, H.J. and GRIFFITHS, C.J. (1977): Coastal erosion in Kunduchiarea. Letter to T.T.C. 4p.HEMED, I. (1987): Seasonal variations in the beach configuration. In "Beach Erosion Along KunduchiBeach, North of Dar es salaam." Report for National Environment Management Council by BeachErosion Monitoring Commettee. pp.26-31.KAPILIMA, S. (1984): Stratigraphic, Palaeontologic and Palaeogeographic analysis of the Jurassic-Cretaceous rocks of the coastal basin in the hinterland of Dar es salaam and Bagamoyo. 77p,Berlin.KENT, P.E., HUNT, J.A. and JOHNSTONE, D.W. (1971): The Geology and Geophysics of CoastalTanzania. Geophysical 6, 101p., HMS stationary office, Inst. Geol. Sc. London.KING (1962): The morphology of the earth, 577p., Hafner, New York.LE PICHON, X and HEIRTZLER, J.R. (1968): Magnetic anomalies in the Indian Ocean and the oceanfloor spreading. J. Geophys. Res., 73(6)LWIZA, K.M. (1987): Waves, tides, currents and wind. In "Beach Erosion Along Kunduchi Beach, Northof Dar es salaam." Report for National Environment Management Council by Beach ErosionMonitoring Commettee. pp.10-25.MUSHALLA, H.M. (1978): Coastal processes along Kunduchi Beach. J. Geog. Ass. Tz. 17.NEMC (1985): Project proposal of Coastal erosion in the recreational area north of Dar es salaam inTanzania. 11p., Doc. 166v (3)/fc.NORRMAN, J.O. (1985): Project proposal on control of coastal erosion in the recreational area north ofDar es salaam. Rep. Min. Lands, Housing and Urban Dev. DSM. 10p.ODADA, E. (1992): Sea level rise causing concerned. Daily Nation Kenya.QUELENNEC, R.E. and IBE, A.C. (1989): Methodology for inventory and control of coastal erosion

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 99in the west and central Africa region. Draft paper <strong>UNEP</strong>.SCHILLER, E.J., and BRYCESON, I. (1980): Beach erosion in the Dar es salaam area. Univ. Sci. J.,4, 101-119.SHEDD, M.L. (1974): Report on the turtles of Maziwi island Tanzania, July-October 1974. unpubl.report, 49p.SHUNULA, J.P. (1990): A Survey on the distribution and Status of Mangrove Forest in Zanzibar,Tanzania. Zanzibar Environmental Study Series, No.5, 1990. Commissionfor Lands and Environment.STUHLMANN, F. (1894): Mit Emin Pascha ins Herz von Afrika. 901p. Berlin.WINDLEY, B.F. (1977): The evolving continents. 385p., London, Wiley.

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<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 108VII. BEACH EROSION NORTH OF DAR ES SALAAMby Kamzima M.M. Lwiza1. INTRODUCTIONThe study area Kunduchi beach, is located at 06 40's and 39 13'E approximately 20 kilometersnorth of Dar-es-Salaam, Tanzania (see Fig.1). It is a shelving beach with a gentle slope (the inclination rarelyexceeds 3 ), protected by inshore reefs and islands giving it a rather complex bathymetry. The mean springtidal range is 2.98m, (Lwiza and Bigendako, 1988). The total catchment is 175 square kilometers (Griffiths,1988). Kunduchi area is interest because of its high economic importance and because it is under heavypressure by man. Its associated mangrove vegetation (described in detail by McCusker, 1975) is an importanthabitat for larvae of fish and crustacea. It is also the site of both the Kunduchi Marine Biological Station ofthe University of Dar-es Salaam, Kunduchi Fisheries Institute and several tourist hotels. Directly behind thebeach there are extensive salt evaporation pans covering more the 200 hectares, and not long ago a pi lotheavy mineral (filimenite, kyanite, garnet, zircon etc.) extraction plant was operating. However, most of thebuilding and development of the area has occurred in the last 25 years.Erosion of the beach posed a serious threat to the beach hotels during 1977 and 1978 (Schiller andBryceson, 1978) although the problem was recognized much earlier. Alexander (1969) observed that theshore erosion generally occurs with increasing intensity from Tanga (near the border with Kenya) southward.Duyverman (1978) made a sedimentological study of black heavy mineral sands in theDar-es-Salaam-Bagamoyo area and observed large seasonal changes in beach profiles during one year.In 1980 a team of scientist and engineers from the University of Dar-es Salaam was formed to lookfor a solution to this problem. Due to the alarming rate of erosion, the team hastily proposed the erection ofgroynes and a revetment at Silversands hotel. The groynes were constructed of coral limestone boulders about500 kg, each. They had an average length of 30 m, a height of 1.5 m, a width of 3 m at the base and I m atthe crest. The spacing between them was 50 m. At African Hotel the groynes were constructed by sand filledplastic tubes with a diameter of 1 m and a length 70 m. The spacing between them being 60 m. Later in 1984the old groynes at Silversands were elevated by 1.5 m with ungraded coral rocks and new groynes wereintroduced in between the old ones and extended to the north right up to Bahari Beach hotel. The spacingbetween the new groyne system varied from 15 to 25 m. Since the second generation did not follow anyparticular recommendation, erosion tended to increase in the area. So, in 1986 the Tanzania NationalEnvironmental Protection and Management Council mounted a research project to (a) find out the amountof sand taken out of the streams feeding into the area, (b) measures beach profiles on a fortnightly basis forone y ear, (c) conduct a sedimentological study of the area, and (d) determine patterns of wind, currents andthe tides. This paper covers objectives (b) and (d) and highlights on the effects of the physical parameters onbeach erosion in Kunduchi area.2. MATERIALS AND METHODS2.1 WINDAn autographic anemometer was installed at Kunduchi Marine Biological Station (KMBS) at aheight of 2 m on 20 January, 1987 and started collecting data on 2 February, 1987. Data was read from themonthly rolls then stored on an Ericson micro-computer.2.2 WAVESThe wave staff was made of a wooden piece of 8 m high graduated at 5 cm intervals. It was placedat about 1 m below datum, 450 m from the sea-water intake of KMBS. Heights and periods of ten

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 109waves were recorded each time a wave measurement was required at 0630 East African Time (EAT).2.3 CURRENTSDrogues were used to track currents. The design was modified version of that used by Harvey (1977)in the same area, see Fig. 2. The length between the float and the drogue was 1.5m. It had to be shortened inorder to avoid getting stuck in shallow waters. Observations were done from 0600 to 1800 East African Time(EAT) for 30 days during the northeast monsoon and southeast monsoon. To supplement the data a currentmeter was also used to measure currents in the Kunduchi creek due to the shallow water depth.Tide: A conventional float- operated Stevens tide gauge (Type A Model 71) was installed at the Dar-esSalaam harbor, in front of the regional Marine Police quarters on 6 July, 1986. The gauge was not levelledto a standard bench mark. So, throughout this report, it has been assumed the zero of the tidal staff at the tidegauge is 1 m below datum.In order to obtain the daily mean sea level values a 30-hour low pass Doodson filter (DoodsonWarburg, 1941) was applied to the data in the following form:_x =and19- 19f i x if i = multiplier of ith hourx i = tide level at ith hourx = tide level at noon of the central dayBeach Profiles: In October 1983 a pilot program for measuring beach profiles was conducted at SilversandsHotel. The engineer's level-and -rod method (Aubrey, 1978) was applied. The concrete platform on the hotelveranda 1 m from the entrance to the bar was used as a bench mark. In order to establish a permanentrange-line, two armored iron rods were placed 40 m apart in a line perpendicular to the shoreline. The innerpole was placed 2 m backshore from the berm crest. Elevations were recorded at 2 meter intervals. Themeasurements were taken once a week during low tide for a period of five months (September 1983 toFebruary 1984 ). Thus covering the whole of Northeast monsoons season .In 1986 Hemed (1988) used a similar method (without range rods) to measure seven profiles in thestudy area. To reduce labor cost profiling was done on a fortnightly basis from October 1986 to August 1987.3. RESULTSWind: During the Northeast monsoon wind speed varied between 1.5 and 8 m/s. The wind blew from theNorth except in the afternoon from 1630 EAT to midnight when it blew from the East. During the Southwestmonsoon the wind had an average speed of 8 m/s with the main direction being from South. For both seasonsthe wind speeds were fairly low, typical of this area. Figs. 3 and 4 are examples of wind roses for Februaryand August, 1987.Waves: In the Northeast monsoon most waves were aligned to the wind direction. Wave action south Mbeziriver was very low, with an average height of 0.2 m. It was low probably because it is in the shadow zone ofboth Mbudya and Pangavini islands. About three kilometers northwards from Mambwe river waves increasedin size (0.4 m) up to African hotel. East of sand spit at Kunduchi waves were choppy and confused causedby interference and the ebbing current form the Kunduchi creekFor the stretch between Kunduchi hotel and Silversands hotel the wave condition was the constantat 0.5 m. Then it started increasing up to Bahari hotel where it was 1.2 m and it stayed high to Ras Kiromoni.Usually in the morning small locally generated waves would be riding on a swell of 6-7 seconds with a heightof 1.3 m. The swell stayed until l000 EAT. The maximum immersed weight of sand transported longshorewas found to be 600 newtons/see

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 110In the Southwest monsoon the waves were not entirely aligned to the wind direction, they were waspredominantly from the Southeast. Coral reefs and the islands play an important role in refracting anddiffracting the waves in this area. The submerged coral reef patches (e.g. Fungu Mkadya ) act like lens byfocusing (i.e.concentrating) wave energy on some particular parts of the beach. The exercise of analysingwave refraction diagrams was not part of this study. However, from few available aerial photographs someareas could be identified to be at high risk. These are: (i) the area between Ras Kiromoni and Bahari hotel,(ii) the sketch between Rungwe hotel and Tegeta stream and (iii) the area northward of Mbezi river for about2.5 km.Even during the Southwest monsoon south of Mbezi river was still a low energy area, average waveheight was 0.5 m. Between Mbezi river and Africana hotel the height was almost double, 0.9 m. The stretchbetween Kunduchi and Rungwe had an average wave height of 1.5 m. The area north of Bahari hotel to RasKiromoni had a 2 m wave height. The maximum immersed weight of sand transported longshore was 10002N/s whereas the average wave energy was 2.5 kW/m which is quite a considerable amount of energy.Current: The drogues were cast about 800 m from the shore in order to avoid getting stuck. On average thedrogues were tracked for 11.5 hours each day. Most of the drogue tracks were restricted within an area notmore than 1.5 km from the shore. Fig. 5 shows a composite plot for selected drogue tracks during theNortheast monsoon. During a tidal period the drogues drifted back and forth parallel to the shore. Themaximum tidal excursion during spring tides (range= 3.4 m) was 6.2 km compared to 2.5 km at neaps(range=0.9 m). The maximum excursion could only be obtained if the drogue was deployed betweenSilversands hotel and Ras Kiromoni just after high water. For example a drogue set 800 m east of KMBS hadan excursion of only 5.1 km. Another interesting feature was the persistent easterly deflection of the droguesduring flooding. A typical example is illustrated by Fig. 6 which shows a drogue track for 20 February 1987.The tidal range was 2.2 m and tidal excursion for the drogue was 5 km.The average speed obtained from drogues over the tidal cycle was 0.25 m/s: maximum speed was0.5 m/s. The results agreed very well with direct current meter measurements with daily maximum speed at0.3 m/s for neap and 0.75 m/s for springs.In the Southwest monsoon, the current pattern did not change very much. There was still an easterlydeflected. Another feature which was not affected by seasons was the current pattern in the Kunduchi creek.Ebbing velocity reached 3.5 m/s while during flooding the maximum velocity was slightly above 4.5 m/s. Themotion was very turbulent and in most cases too strong for the boat to anchor. Also the bed is formed bycoarse sand which is very loose. Although the main channel is oriented in an east-west direction parallel tothe Kunduchi sand spit, the flood tide drives the current into the creek from south-southeast. During ebb thecurrent starts by flowing parallel to the spit but as it gains speed it becomes more turbulent with a generaldirection changing to east-southeast.North of the spit, much closer to the shore the ebb current flowed parallel to the shore towardsAfrican hotel. This might affect sediment transport in the vicinity of the hotel especially the northern endduring the Northeast monsoon when the creek current is most significant. Figs. 8 and 9 show a general currentpattern during ebb and flood, respectively.Tide: The annual mean sea level was 1367 mm above datum. The maximum mean sea level was 1487 andthe lowest was 1264 mm. The daily mean sea level (MSL) kept fluctuating throughout the year, see Figs. 10and 11. Some changes were spectacular, for example a drop of 160 mm in MSL on 13 August, 1986. Thedrop is equivalent to an increase in the atmospheric pressure of 16 mb. There are also strong 10 to 30 dayfluctuations in the tide gauge records but 30 day period tends to dominate.Beach Profiles: All Silversands 1983/4 beach profiles had uniform concave shape. In Figure 12 time seriesof spot levels of 1983/4 data from one position for 125 days. There are bouts of erosion and accretionoccurring in succession within a period of 33 to 35 days. However there is still an observable net erosion.Results from Hemed(1988) show similar features with erosion immediately followed by accretion of almostthe same amount. There was no discernable period from the time series of Hemed's profiles.4. DISCUSSIONThe year in question, 1987, was a typical year according to the wind figures 2 and 3. There are nomarked differences from previous years (c.f. Niewolt, 1987). The wind energy along the Kunduchi beach is

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 111low. Occasionally it picks enough strength to form sand dunes and erode the backshore. Erosion occurs duringboth seasons but it is more severe during the Southwest monsoons when the wave energy is higher. Episodicevents like the storm surge of August 7, 1987 cause more damage than the normal erosion-accretion cycle.Tide is a wave riding on the mean sea level and therefore any change in MSL is important to the beachmorphology. Daily changes in MSL have been observed to reach 200 mm. This can affect the tide a greatdeal. There are several factors that can affect the MSL, e.g. storm surge, atmospheric pressures changes andseiches. In the tropics meteorological tidal forcing is such that the diurnal frequency is driven byanchor-offshore winds and the semi-diurnal frequency is by atmospheric pressure (Pugh, 1979). However,a low-pass filter eliminates errors with short periods like seiche and S2 components of radiation tides. It isvery likely that the strong 30 day fluctuations in MSL are caused by wind driven Kelvin waves similar toobservations made in the Pacific (Miller et al.,1988). Therefore the frequency 0.30 cpd observed in 1983/4data of beach profiles at Silversands Hotel is most probably also a response to the forcing of zonalatmospheric wind. The 30 to 60 day oceanic response has been observed elsewhere in the Western IndianOcean, (Schott et al.,l988). Investigators (e.g. Nummedal et al., 1984) in beach morphodynamics when theysay the energy spectrum is dominated by long-period infragravity oscillations they normally refer toedge-waves. However, this study has shown that longer periods (~30 days) are also important in themorphology of Kunduchi beach. The 1986/7 beach profiles do not show a 30 day cycle probably due tolevelling to the method used, since the profiles were measured on a fortnightly basis Also there was nocorrelation between mean sea level changes and erosion measured from beach profiles because, first, springhigh water does not necessarily coincide with maximum sea-level, and second, the beach profiles weremeasured on a fortnightly basis. So a profile measured on a particular day could have been caused by an eventwhich took place ten days earlier.An intriguing question has always been to know where the sand goes from Kunduchi. Bird (1985)and Griffiths (1988) proposed that the sand is transported by longshore drift past Ras Kiromoni into UnunioBay. Most drogues described 8-shaped tracks with a net displacement offshore. This confirms the hypothesisput forward by Norman (1985) that a good percentage of the sand was going offshore. It is supported alsoby the fact that Ras Kiromoni acts as a point of divergence during the ebb tide and convergence point at floodtide. Therefore one would expect a lot of sand transport past the headland from the south into Ununio bayespecially during the Southwest monsoon but there was no sign of sediment transport. For more than 1.5 kmsouthward of Ras Kiromoni there is no beach, the 4 m cliff more or less falls straight into deep water (ca. 7m), the sea-bed is extensively covered by sea-grasses (especially Syringodium thallasodendron ) and the currentat mid-tide reaches 0.75 m/s. Seldom, does the sand pass this point that it actually does not interfere with thegrasses. The only possible way for the sand to reach Ununio bay would be to go offshore first and then,maybe, move back inshore by wave action thus bypassing Ras Kiromoni. Therefore it seems the sand iseroded from the beach by longshore drift then deposited offshore by the tidal current at the following sites:(i) area between Bahari hotel and Fungu Mkadya, (ii) in front of Kunduchi creek. The latter is moresignificant than the former because most sand eroded from the south is caught by the creek. Some sand isused to build up the sand spit, the rest goes offshore. How much goes offshore is not known yet but it is mostlikely that more is transported offshore because it has been found elsewhere that in small tidal creeks ofmesotidal swamps sediment transport is predominantly seaward (Kennedy and Pinkoski, 1 987).Several reasons have been given for the marked increase of beach erosion in the area. Someinvestigators propose that the damage to the reef by dynamite fishing has reduced the barrier height whichused to protect the beach from the battering action of waves. Another proposed cause is the hauling of sand3for construction from the streams feeding into the area; Griffiths (1988) estimates 100,000 m are extractedannually. Visual inspection of the coral reef platform around the islands showed that despite the crater-likepot holes on the seaward side, caused by dynamites, there was no appreciable decrease in the platform levelto change the wave pattern. The average width of the barrier reef in the area is about 200 m. Therefore wecan conclude that the rate of beach erosion at Kunduchi has increased in recent years because of (i) sandmalnourishment caused by extraction of sand from the streams and (ii) intensification of isostatic adjustmentof the land which is assumed to be responsible for the submergence of Maziwi island (in the north nearTanga) in 1981. Dynamite fishing has very little effect if any on beach erosion. Future research shouldconcentrate on determining the amount of sand going offshore. Also it is important to explore the role ofcoastal-trapped Kelvin waves and quantify the effects of isostatic adjustment so that they can be distinguishedfrom sea-level rising effects.In order for the sea-level and erosion monitoring programs to work we need to select two or threepilot projects where erosion is acute, but the area should be readily accessible. The program should measure

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 112the following parameters: beach profiles, atmospheric pressure, sealevel, temperature and salinity. Along within situ measurements other means, especially remote sensing techniques like aerial photographs and satelliteimages should be employed. We should also try to develop hydrodynamical models incorporating sedimentdynamics and use them to asses various remedial scenarios. This will provide environmental managers witha much needed tool for objective management policies.ANNEX IREFERENCESALEXANDER, C.S. (1969). Beach ridges in northeastern Tanzania. Geogr. Rev. 59,104-122AUBREY, D. (1978). Statistical and dynamical prediction of changes in natural sand beaches. PLD thesis,University of California, S an Diego.BIRD, E. C.F. (1985) Coastline changes: A global review. John Wiley & Sons Ltd., Chichester pp219DOODSON, A.T and WARBURG, H.D. (1941). Admiralty Manual of tides. Hydrography department.Admiralty, London.DUYMERMANN, H.J. (1978). Sedimentology of black sands in the Dar-es-Salaam-Bagamoyo area.UNESCO Rep. (URT/72/003).GRIFFITHS, C.J (1988). Impact of sand extraction from seasonal streams on erosion of Kunduchi Beach.In Beach erosion along Kunduchi beach, north of Dar-es-Salaam: Rep. for Tanzania NationalEnvironment Management Committee. ppS3HARVEY, J.G. (1977). Some aspects of hydrography of the waters off the coast of Tanzania: acontribution to CINCWIO. Univ. Sci. J.(Dar. Univ). 3.53-92.HEMED, I.A. (1988). Seasonal variations in the beach configurations. In Beach erosion along Kunduchibeach, north of Dar-es-Salaam: rep. for Tanzania National Environment Management Committeeby Beach Erosion Committee. pp.53 KennedyLWIZA, K.M. & BIGENDAKO P. R. (1988). Kunduchi Tides. Tanz. J. Sci., 14McCUSKEr, A (1975). The Kunduchi mangrove basin. Dar Univ. Sci. J.(Dar Univ), Vol 1(1),D30-41MILLER L., R.E. CHENY, and B.C. DOUGLASS (1988) Geostat Altimeter Observations of Kelvinwaves and the 1986-87 El Nino. Science, 239.52-54NIEWOLT, S. (1973). Breezes along the Tanzania coast. Arch. met. geophys. bioclimate.,l6,122 132NORMAN, J.O. (1985). Project proposal on control of coastal erosion in the recreational area north ofDar-es-Salaam. Rep. Min. Lands,NEMMEDAL,D., D.L SONNENFELD and K. TAYLOR (1984). Sediment transport and morphologyat surface zone of Presque Isle, Lake Grie, Pennsylvania In:B.Greenwood and R.A. Davis, Jr.(editors), Hydrodynamics and Sedimentation in wave dominated coastal environments. Mar. Ged.,60:91-122PUGH, D.T.(1979), Sea levels at Aldabra atoll, Marbasa and Mahe western equatorial Indian Ocean.Deep Sea Res. 26:237-58SCHILLER E.J. and I. BRYCESON (1978) Beach erosion in the Dar-es-Salaam area. Univ. Sci. J.(DarUniv). 4(182),101-19SCHOTT F., M. FIEUX, J.SWALLOW and R.ZANTOPP (1988) The boundary currents east and northof Madagascar, Direct Measurements and model comparisons, J.Geophys. Res. 93.4963-74

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<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 124VIII. LITTORAL SEDIMENT MANAGEMENTby Otavio Sayao, P.Eng.WORKSHOP NOTES Presented atThe <strong>UNEP</strong>/CNA <strong>Workshop</strong> on Coastal Erosion, Maputo, Mozambique, December 1 -3,19931. LITTORAL SEDIMENT MANAGEMENT1.1 INTRODUCTIONIn order to undertake a coastal zone management plan (CZMP), a basic understanding of littoralsediment processes, management and control is needed. This paper presents a review of littoral sediments andprocesses for sandy shorelines. More comprehensive reviews of littorai processes are available in theliterature, such as given in Zenkovich (1967), King (1972), Silvester (1 974), Komar (1976), Bowen (1980),Sayao and Kamphuis (1983), Komar (1984), U.S. Army Corps of Engineers (1984) and Horikawa (1988).In Canada, the Ontario Ministry of Natural Resources (MNR) has recently sponsored a shorelinemapping campaign for the Great Lakes, as well as two coastal engineering studies which would providebackground data for future coastal management plans: a wave climate database for the Great Lakes (MNR,1988a; 1 988b; 1 988c) and a general shore sediment study (MNR, 1 988d). The Great Lakes shorelinecomprises about 1 0,000 km and correspond to 4% of Canada's total coastline. As shown in Tables 1 and 2(from Ibbott and Whittington, 1991) the amount of money spent by Canada on its shorelines in 1988 wasapproximately $1 billion. The portion of shoreline expenditure in the St. Lawrence and Great Lakes is about40% of this total, which justifies the general concern with land and properties erosion losses, and thus theneed for management procedures.1.2 SHORE MORPHOLOGY CLASSIFICATION FOR THE GREAT LAKESGeneral shore morphology information for the Great Lakes may be obtained from the Coastal ZoneAtlas (Haras and Tsui, 1976). More detailed site-specific information (such as shoreline structuresinventories, shoreline recession rates, etc.) is recently available, and all of this information will form part ofa Geographical Information System (GIS) database (Law et al., 1 991). The basic shore types may beclassified into five groups (MNR, 1988d):1. Sandy2. Composite3. Cohesive Material4. Rock5. MarshSandy shore is defined as the shoreline composed of cohesionless material of sufficient thickness toprovide protection to underlying tills or backshore bluffs from wave attack. Cohesive material mainly refersto glacial till, clays and silts. Composite is defined as cohesive material overlain by a thin layer of sand,insufficient to provide any degree of protection from wave induced erosion (Kamphuis, 1986). Marshy areasare classified separately because of the unknown nature of sediment types within these areas.

Tables 1 and 2Exhibit E.1Spending On Shore and Nearshore Facilities, 1988 (5, 000)<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 125Activity Atlantic St. Lawrence Paciflc Arctic TotalGreat Lakes_______________________________________________________________________________Harbours, 207,062 193,143 121,500 10.307 532,012Waterways &Navigation_______________________________________________________________________________Oil & Gas 31,700 673 --- 115,000 147,373Exploration andProduction_______________________________________________________________________________Industry and 8,867 46,339 16,910 --- 72,116Public Utility_______________________________________________________________________________Aquaculture 20,148 6,130 7,811 --- 42,089_______________________________________________________________________________Municipal Water- 27,701 104,756 24,329 --- 156,786front, Marina &Yacht ClubDevelopments_______________________________________________________________________________Erosion 3,309 77,683 2,550 1,000 84,542Protection_______________________________________________________________________________Habitat 1,550 4,676 1,102 --- 7,328Enhancement_______________________________________________________________________________All Activities 308.337 433,400 174,202 126,307 1,042,246- less than $ l,000 identified.Exhibit E.4Average Annual Rates of Land Losses to ErosionArea Lostm 2Nova Scotia 650,000Prince Edward Island 260,000New Brunswick 500,000Lake Ontario 70,000Lake Erie 290,000Lake Huron 50,000Beaufort Sea 1,500,000Strait of Georgia 10,000NE Howe Island 25.000________Total 3,355,000The definition of the sand lower boundary differs in literature. Therefore, discrepancies may occurfrom one reference to another, in the amount of sand present at a given area, because of inconsistentclassification systems. Figure 1 iliustrates the grain size scale for the Unified Soils and WentworthClassification systems. For example, work by Rukavina (1976) defines sand/silt boundary based on Shepard's(1954) classification at the 4 phi (0.063 mm) boundary. This boundary is smaller than sand normally foundon beaches in the Great Lakes, which approximately 2 phi (0.25 mm) above water (Boyd, 1981). Any further

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 126work in this field should be based on one system that defines the lower limit of beach sand at a valuerepresentative of that found in the Great Lakes beaches (0.1 5 mm, for example).A classification system for nearshore slopes on the Great Lakes was put forth by Boyd (1981 ) as:Group 1 -Group 2 -Group 3 -Group 4 -Extensive sand deposition with a number of active large sand bars within 500 metres fromshore.Extensive amounts of sand and bars nearshore but dominated by silts and clays offshore.Little sand nearshore, of insufficient quantities to maintain an appreciable dry beach.Usually found in front of eroding glacial bluffs.Devoid of sand and nominated by till or lag deposits and bedrock.Figure 2 shows the 4 types of profiles (from Boyd, 1981). There are many locations around the Great Lakeswhere sand deposits are found to be completely contained between rocky headlands. Such deposits are 'relict'remnants from old glacial lake beaches, left behind when the glaciers retreated (Boyd, 1981).1.3 LITTORAL CELL BASICSGeneralA littoral cell is a section of coast where no inflow or outflow of sediments takes place across it'sboundaries. A cell is a self-contained coastal system where the on-going shoreline processes do not affect,and are not affected by, the processes of neighbouring cells. The definition of the littoral cell limits is essentialto the development of a SMP, for the natural coastal processes may be quite different from cell to cell, alongthe same stretch of shoreline (Figure 3, from MNR, 1988d).Littoral transport in the nearshore zone is the movement of beach sediment both parallel to the shore(longshore) and perpendicular to the shore (cross-shore), under the influence of waves and currents. Thelongshore limits of a littoral cell are defined by natural formations or artificial (manmade) barriers, where thenet sediment movement changes direction or becomes zero.Subcells and Non-Drift ZonesLittoral cells may contain smaller structures or headlands that act as partial barriers to transport; somelittoral sediments bypass these barriers. Segments of shoreline between partial barriers are referred to assubcelis. Most of the littoral cells in the Great Lakes have been artificially segmented into subcells byman-made structures (Smith and Sayao, 1989). It is thus important to distinguish these from the naturalsubcells that occur where headlands partially block the littoral drift.The definition of 'littoral cell' implies that littoral sediments are moving within the cell. There are,however, many areas around the Great Lakes where the supply of littoral sediments is limited to the extentthat very little actual transport occurs. Current and wave action still occurs in these locations and would, givena supply of sediment, induce sediment transport. Therefore, even though shoreline features and structurescould function as a potential barriers within these areas, (i.e., littoral cells exist by definition), it would bepointless, from a shore management perspective, to identify littoral cells in the absence of longshore transport.Sections of the shoreline that are characterized by the above are called 'non-drift zones'.Human InfluencesBarriers to littoral transport can be either natural (e.g., rock headlands or sediment sinks) or manmade(e.g., harbour piers). The natural barriers have been in existence for several thousands of years. Man-madestructures have only been in place for the last hundred years or so, and they will likely disappear within thenext few hundred years (although new structures will undoubtedly be constructed). However, while they exist,these 'artificial' barriers may alter the natural transport patterns. For examp le, the Goderich Harbour piersand dredged navigational chan nel on Lake Huron now act as total barrier and form the limit of two separatecells (Figure 4, from Smith and Sayao, 1989). Before these features were built, a single natural cell existedfrom McRae Point in the north, to Kettle Point in the south. Sediment derived from the high bluffs north ofGoderich can no longer be transported south of the harbour. Similar examples of man's influences on theshoreline may be observed in the Eastern Beaches (see Figure 5) and Scarborough Bluffs areas of the Toronto

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 127waterfront.Sources and SinksThe area of the littoral cell where sediments accumulate is called a sediment sink. The source ofmaterials in the littoral cell is the location where sediments are available to be erode or transported.Primary sediment sources in the Great Lakes are the shore bluffs and nearshore lakebed, however,gully erosion, river discharge and artificial nourishment activities may also be significant sources in someareas. The offshore zone may act as source of littoral material due to seasonal and storm induced profilechanges and to erosion of the nearshore bottom and beaches.Major sediment sinks occur in areas of low wave energy and include (Figure 6, from MNR, 1 988d):accreting natural beaches;offshore shoals;fillet beaches due to man-made littoral barriers;shoals or tombolos due to offshore structures, andareas of dredging or mining activities.Dredging and mining can have significant impacts on sediment budgets and littoral processes.Material is lost to the littoral zone when dredged from navigable waters (channels and harbour entrances)within a littoral cell and dumped outside the littoral cell, such as at landfill areas or in deep water.The offshore zone may also act as a potential sink. Typically, the finer-grained silts and clays aredeposited in the offshore area but sand transport to the offshore may occur as a result of:storm waves which stir up sand, particularly when onshore winds create a return lake flow;turbulent mixing along the sediment concentration gradient which exists between thesediment/water mixture of the surf zone and the clear water offshore;the slight offshore component of gravity which acts on both the individual sediment particlesand on the sediment-water mixture; andcomminution of sand grains.1.4 LITTORAL PROCESSESIntroductionThe movement of sediment in the nearshore zone by waves and currents may be divided into twogeneral types: transport parallel to the shore (longshore transport) and transport perpendicular to the shore(cross-shore transport). Sediment movement resulting in erosion or accretion of a beach section is actuallyan interaction of these two types of motion.The transport of sediments parallel to the shore in the surf zone is called littoral transport and iscaused by obliquely incident waves. Figure 7 shows a schematic diagram of the two mechanisms for thelittoral transport:(a) beach drifting in the swash zone, and(b) bed and suspended load transport in the breaking zone.The two-phase flow phenomena are different in the nearshore zone, in the continental shelf (offshorezone), in rivers and in estuaries so that different theories exist for the estimation of sediment transport rates.The modelling of littoral processes will be briefly presented in the following sections.Cross-shore sediment transport is the movement of material perpendicular to the beach both in theonshore and offshore directions, causing beach profile accretion and erosion. Figure 8 shows the cross-shoretime scales (from Stive, 1991). The interaction of longshore and cross-shore sediment transport has been thesubject of a great deal of research efforts recently, both for short and long term shoreline evolution studies.

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 128Figure 9 shows one approach towards the analysis of sediment transport (from Kraus, 1991). Recent workon modelling morphological problems in the coastal area are described in Larson et al., (1990), Hanson andKraus (1989) and de Vriend (1991), among several others. The classification of the shoreline models is shownin Figure 10 (from Kraus, 1989).Sediment SupplyThe existing methods to calculate littoral transport rate assume that an infinite amount of sand isavailable in the beach. Usually this is not the case and thus it is necessary to distinguish potential transportrates (resulting from calculations using these expressions) from actual transport rates, the amount of materialactually moving along the shore.Potential longshore transport rates may be calculated using both the CERC expression (U.S. ArmyCorps of Engineers, 1984) and the Queen's formula (Kamphuis et al., 1986). The Queen's formula has theadvantage to take into account the wave parameters as well as beach slope and sediment grain size. This isfurther discussed in the next sections.The intermittent, thin, narrow beaches that are characteristic of some littoral subcells in the GreatLakes are indicative of a sediment deficit. That is to say that the actual wave energy which is available totransport beach-sized sediments (i.e., sand and gravel) both cross-shore and longshore, exceeds the actualsupply of sediments. The actual supply of beach sand and gravel from the eroding bluffs is a relatively smallpercentage of the total volume. The bulk of the volume consists of silts and clay and these fine materials aretransported offshore out of the littoral system. There is not enough of the remaining coarser materials toprovide sufficient protection against erosion to the underlying cohesive profile during periods of high waterand/or severe storms.A procedure to calculate actual sediment transport rates has been recently proposed in Kamphuis(1990a). It assumes that sand is only available to be transported to a certain depth h (see Figure 11 ) and thusthe wave energy offshore of 'h' is not accounted for in the littoral drift computations.Sediment BudgetIn order to fully describe the littoral processes occurring along a particular stretch of shoreline, it isnecessary to estimate the amount of sediment transported, its origin and where it is deposited. The systemaccounting for the quantities of littoral transport is called the sediment budget. The sediment budget gives anestimate of material entering the littoral zone from each source, and the amount of sediment deposited at eachsink or barrier along the shore. The sediment budget must balance. That is, the total amount of supply mustequal the total amount deposited plus the amount still in transport. Typically sediment budgets are concernedwith the long-term transport rates and transport patterns. However, it must be noted that short-term impactsmay be significant and should also be accounted for. Thus, the estimation of the short-term transport patternsare also important.Shore bluff recession rates have been measured for most of the shorelines around Lake Ontario, LakeErie and Lake Huron. Boyd (1981 ) conducted measurements of bluff recession rates between 1973 and 1980for the Great Lakes shorelines using erosion-monitoring stations data. Other information collected includedgrain size analyses, descriptions of vegetation cover and existing shore protection works. From the surveyinformation, annual volumetric erosion rates (volumetric change per unit height per unit length/per year, in3m /m/m/y) were calculated for similar reaches of shore bluffs. Also, after making allowances for thepercentage of sand and gravel (littoral material), and after accounting for the percentage of shore that isprotected, the amount of sediment input to the littoral zone from shore bluff erosion was estimated, i.e. thesediment supply.The erosion monitoring programme, described by Boyd (1981) was discontinued in 1980, so theestimate values are based on seven years of data. Ideally, such surveys should be based on a continuousrecord of shoreline position, rather than on localized data from monitoring stations. It is recognized thatnearshore sounding surveys need to be conducted in erosion prone areas, in order to estimate the amount oflittoral sediment contributed from subaqueous erosion. It is possible that in some areas the amount of sedimentcontributed from nearshore erosion is of the same order of magnitude to that of shore bluff erosion.

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 1291.5 BEACH PROFILESIntroductionBeach profiles are classified according to their seasonal variations in three basics forms (Figure 12):- the bar profile, or the storm profile (also referred to as the 'winter profile') formed by wavesof high steepness, with a milder foreshore slope and one or more bars depending on waveand grain size characteristics;- the step profile, or the berm profile (also referred to as the 'summer profile) formed by wavesof low steepness, with a steeper foreshore slope and no bars; and- the welded bar profile (Sunamura, 1989), a neutral profile that transforms itself into both thebar and the step profiles depending upon the wave conditions.Several criteria for on-offshore transport in sandy beaches are given in literature:(1) the criterion proposed by Iwagaki and Noda (1962). where the line of transition is a functionof the parameters H 0 / L 0 and H0 / D 50;(2) the criterion proposed by Dean (1973), in which the transition is a function of the dimensionless falltime parameter, H b/(wsT), where w s is the fall velocity of the grains. Since most of the available datasets presented the measured value of the deep water wave steepness, rather than the breakersteepness, Dean's (1973) correlation was based on plotting H /L versus ( w )/(gT). Also, the Shore0 0 sProtection Manual (U.S. Army Corps of Engineers, 1977; based on Kohler and Galvin, 1973) showsresults of the prediction of profile types based on a deep water fall time parameter, F 0 = H 0 /(wsT),where for F 0 < 1 profile accretion occurs and for F 0 > 1 to 2 erosion is most likely;(3) the criterion proposed by Sunamura and Horikawa (1974), where beach erosion andaccretion is a function of 3 parameters: deep water wave steepness, the ratio of grain size to deepwater wave length, D/L , and bottom slope; and02 2(4) Sunamura (1984; 1989) criterion based on the parameter K = H b /(gT D).(5) Kraus et al., (1991) criteria, including a new Froude-type parameter w / sqrt (g H )/ which iss 0a combination of H /L and F to predict beach erosion and accretion.0 0 0Figure 13 (from Sayao and Graham,1991) shows the 3 typical profile regions of Sunamura (1989)and field data from Takeda and Sunamura (1982). This on-offshore criterion is similar to the one by Iwagakiand Noda (1962). The equations for the demarcation of field and laboratory profiles are also shown in Figure13. However, Sunamura (1989) found different trends for field and laboratory data, with no apparent reasons.Beach Slope DefinitionsThe foreshore slope of the beach under the wave swash zone, also called the beach face slope, wasfound to be related to median grain size D 50 (Wiegel, 1964; King, 1972; Bascom, 1980). A steep foreshoreslope corresponds to coarse sandy beaches, and a flat beach face is an indication of finer material. The degreeof exposure to wave action was also found to be a factor affecting the foreshore siope (Wiegel,1964;Komar,1976; Bascom,1980). The beach face becomes flatter when eroding and steeper when accreting.Wave action on beach profiles has been the topic of many investigations in two dimensionallaboratory flumes, both with plane fixed slopes or movable bed beaches. This topic was reviewed in Sayao(1982). The plane initial beach slope is tanß where ß is the angle above the horizontal. The movable bedbeach slope m, which develops under wave action inside the breaking zone, may be defined as:m= d / (1 )b bwhere d b is the breaking depth and b is the breaker distance. Figure 14 shows the terminology usedhere related to beach profiles and surf zone processes. As long as the breaking point location is defined inevery test, the beach slope m is also determined. With the development of a movable bed model experiment,the beach slope is constantly changing with time and dynamically adjusting under wave action. Thus, onbeach studies m should not be mistaken for tanFor prediction purposes it is necessary to have some means of schematizing the beach profile. The

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 130definition of the various slopes related to the surf (active area of beach profile) is only possible if the positionof the breaking point is defined. The breaking point position is usually the position along the beach profilewhere the wave height is maximum. Breaking wave height measurements in a 3-dimensional movable bedmodel were made by Sayao (1982; see also Sayao and Kamphuis, 1982). The breaking point position wasobtained by changing the position of the probe near breaking and observing were the maximum valueoccurred. The breaker distance Ab was defined in the modei as the horizontal distance from the breakingpoint to the shoreline, at still water level (SWL). Thus, Lambda, was determined from the plotted beachprofiles and did not depend on visual measurements.An equation for the prediction of beach profiles was presented in Sayao and Graham (1991 ) for bothfield and laboratory data:H b H b-1/4 -1/4m=0.10(----) (----) (2)D L 0This relationship was developed based on the work of Sunamura (1984) and agrees with his data setas well. For engineering applications it is important to note that different definitions for beach face slope andbeach profile would yield different slope values.Dean (1977; 1990) studied beach profiles along the East and Gulf Coasts of the USA and developeda general formulation for equilibrium beach profiles that can be useful in a number of coastal engineeringmodelling applications (Figures 15 and 16):2/3h = A x (3)where h is the water depth at a distance x from the shoreline and A is the sediment-dependent scaleparameter. Figure 17 (from Dean, 1990) show the characteristics of beach profiles in and out of equilibrium.Kemp (1960, 1962) showed that the ratio between the wave uprush time tut measured between thebreaking zone and the limit of uprush, and the wave period T influences coastal processes. His resultsdemonstrated the importance of the 'phase difference' parameter t /T in relation to the beach profile type:ufor low t u /T, a step profile is formed whereas for high t u /T, a bar profile develops. The relationship betweenwave action and beach slope for low phase differences was investigated by Kemp and Plinston (1968) forcoarse sands. The results showed that the beach face slope and the width of the surf zone are dependent onthe breaker height and on the wave period. Further experimental evidence of the influence of the wave periodon the beach profile formation was given by Sitarz (1963) and Motta (1964).1.6 SEDIMENT TRANSPORT MODELLINGIntroductionA sound approach to coastal processes studies is to couple local experience with coastal engineeringmethods (numerical models). In this context, Kraus (1989) has succeeded to summarized in writing theapproach towards solving coastal engineering problems:"The best 'model' is to know the optimal project design from experience. Because of thecomplexity of beach change, design decisions should be grounded on "empirical modelling," i.e.,adaptation and extrapolation from other projects on coasts similar to the target site. Coastalexperience and understanding of coastal processes (wave, currents, sediment transport) andgeomorphology are essential. However, prediction through coastal experience without the supportof an objective, quantitative tool, such as numerical model, has limitations:a. It relies on the judgement of specialists familiar with specific regions of the coast and onexperience with previous projects, which may be limited, inapplicable, or anachronistic.b. It is subjective and does not readily allow comparison of alternative designs withquantifiable evaluations of relative advantages and disadvantages. Also, conflicting opinionscan lead to confusion and ambiguity.c. It is not systematic in that it may not include all pertinent factors in an equitable manner.

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 131d. It does not allow for estimation of the functioning of new, novel, or complex designs. Thisis particularly true if the project is built in stages separated by long time i ntervals.e. It cannot account for the time history of sand transport as produced, for example, byvariations in wave climate, modifications to coastal structures, and modification of the beachf. It does not provide a methodology and criteria to optimize project design.Finally, complete reliance on coastal experience places full responsibility of project decisions on thejudgement of the engineer and planner without recourse to external and alternative procedures."Littoral Transport ModelsThe available literature regarding littoral transport of sand by waves is extensive and a review showsthat many theories and expressions for the prediction of littoral sediment transport rate exist (Sayao andKamphuis,1983). Analysis of the littoral sand transport volumes and rates may be approached in two ways:(i) by relating directly to wave parameters such as wave energy flux (or wave thrust),(ii) by modification of river sediment transport formula for the coastal zone.The so called 'Wave Energy Flux Approach' is one of the methods of analysis of littoral transport.It is based on wave energy flux and similar relationships, and results from early empirical developments. Asstated by Longuet-Higgins (1972): "it represents the pioneer's first intuitive attempt at grasping the quantitylateral wave thrust".Similarly, another method of analysis may be based on modifications of river sediment transportformulae, the 'Steady Flow Modification Approach'. Einstein (1948) suggested a basic similarity between thesand movement on a beach and in a river. He said: "The motion of sand along a beach resembles in manyrespects the motion of a sand in a river. This latter problem has been solved in large part, and it is reasonableto expect that a solution of the beach problem might be found by application of these same principles". Inriver engineering there are numerous sediment transport theories, often evaluated for limited ranges ofsediment sizes and hydraulic conditions. A review of some of these theories may be found in White et al.,(1975). Some recent modifications may be found in van de Graaff and van Overeem (1979) and in Swart andFleming (1980). Their reliability may be summarized with van de Graaff's (1980) own words: "The questionof the most reliable prediction technique is probably for the moment a matter of 'belief', however, not everynew technique is automatically better than an older one".These methodologies are also referred in literature as:Bulk-energy predictors, such as the CERC formula (U.S.Army Corps of Engineers, 1984)or the Queen's formula (Kamphuis et al., 1986; Kamphuis, 1990b); andDetailed predictors, such as the ones developed in Bijker (1971), Willis (1979) and Nielsen(1979), among others.All predictive methods for littoral sand transport rates and volumes are based on field and laboratorydata points. Some of the data sets available in the early 1970's were compiled by Das (1971). The need forfield measurements was identified in the United States and Japan, were major studies were carried out, whichincluded extensive data collection at several beach sites. In the USA, the NSTS (Nearshore SedimentTransport Study) was reported in Seymour and Duane (1978), Seymour and Gable (1980) and otherpublications. In Japan, the NERC (Nearshore Environment Research Center) program was carried out from1976 to 1982 and was reponed in Horikawa (1988) .Further random wave measurements (both outside and inside the surfl in the laboratory and in thefield are now available for comparison of prediction techniques, including various publications on DUCK82 and DUCK 85 field data sets (see Figure 18, from Birkemeier,1991), Thornton and Guza (1986) field datafrom Leadbetter Beach (NSTS), Hotta (1980) and Hotta and Mizuguchi (1986) field data from the Japanesecoast (see also Horikawa, 1988).Essentially, to compute littoral drift, the following steps are necessary:Deep water wave climate input data, available from NMR wave hindcast.

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 132Shallow water wave transformations are then performed, leading to the definition of breakingwave climate.Littoral transport rate calculations are performed. For this, detailed surficial sediment data andbeach profile data are needed, as well as breaking wave conditions.Nearshore sediment transport models include algorithms for the calculation of:roughness and friction of bottom sedimentslongshore currentslittoral driftcross-shore transportRecently, these modelling techniques were used in the Canadian Coastal Sediment Study (C2S2).This was a research oriented study of sand transport on two Atlantic beaches carried out by the NationalResearch Council of Canada over 4 years (1982/1986). Most of the available transport rate predictors wereused in this study. A discussion of results, conclusions and recommendations are reported in Willis (1987).The Bijker (1971) method did not show consistent results during the C2S2 study, and is very sensitiveto the roughness values used. Sayao et al., (1987) have shown how sensitive sediment transport equations maybe to roughness and friction parameters. This has been known for several years (Bijker, 1971) and is still thesubject of further research. Also, the Nielsen (1979) formula is very sensitive to wave diffusivity and needsas input data the distribution of the suspended sediment transport concentration, a difficult parameter tomeasure or guess. However, we will investigate the option to use both formulas during the study.The Wave Energy Flux ApproachAn expression for predicting longshore sediment transport rate by waves has been in general use inthe United States since the 1950's. Watts (1953) made the first field measurements relating longshore sandtranspont to local wave characteristics He measured the rate at which sand was being pumped to bypass SouthLake Worth tidal inlet, in Florida, and found that the volumetric littoral transport rate wasa function of the longshore wave energy flux factor. This factor may be expressed as follows:12P l = --- g H b n b C b sin 2 b(4)16where n is the energy flux coefficient, H is the wave height (subscript b denotes breaking waves),is the water density g is the gravity acceleration, C = L/T is the wave celerity, L is the wave length, T is thewave period, b is the breaking angle. Watts (1953) used significant wave height when evaluating Equation4 to obtain P ls. Caldwell (1956) measured the rate of erosion downdrift of a littoral barrier at Anaheim Bay,California. Using Caldwell's and Watts' data, Savage (1962) found:Q s' = 4100 P ls(5)where Q s' is the volumetric littoral transport rate in cubic yards/year and P ls is the longshore waveenergy flux factor in ft-lbs/sec/ft of beach. P ls can be calculated using Equation 4 with H defined as significantwave height. This equation was adopted by the U.S. Army Corps of Engineers as an earlier version of whathas become generally known as the 'CERC formula'.Bagnold (1963) proposed a theory in which wave energy was expended to suspend and support thesand particles above the bottom, and any unidirectional current superimposed on the orbital wave motionscould transport sand and produce a net drift in the direction of the current. The relationship may be expressedas:v aI a = K' P __ (6)u owhere I is the immersed weight sediment transport rate per unit width, at an angle a to the waveacrest, K' is a dimensionless constant, P is the available power from the wave motion, v is the unidirectionalacurrent at an angle a to the wave crests, and u is the orbital velocity of the waves at the bottom. Equation 60was further developed by Inman and Bagnold (1963), Komar and Inman (1970), and Baillard (1981).

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 133CERC Formula for Littoral TransportInman and Bagnold (1963) suggested the use of the immersed weight longshore transport rate 11,rather than a volumetric transport rate Q'5. The two are related using the following expression:I = (1-p) Q ' (7)lsswhere p is the beach sand porosity (p - 0.4 for quartz sands), and s in the underwater specificweight of the grains. The immersed weight longshore transport has the units of power or energy flux,and thus may be related directly to the wave energy flux factor Pls. In 1973, based on the field data by Komarand Inman (1970), the CERC formula for littoral sand transport was updated from its earlier version(Equation 5) to read (U.S.Army Corps of Engineers, 1977):Q s' = 7500 P ls(8)where Q s' is the volumetric rate of littoral transport, in cubic yards/year, and P ls is the wave energyflux factor, in ft-lbs/sec/ft of beach, calculated using significant wave height H s .Using Equation 7, the CERCformula may be written in terms of the immersed weight of sand moved, (Vitale, 1980; Bruno et al., 1981)as:I = K P (9)l p lrwhere P lr is calculated using the root-mean-square wave height H rms. I l is expressed in N/s and P lr inN-m/s-m. K p is a dimensionless constant, equal to 0.77 for significant wave height data and 0.39 forroot-mean-square wave height data. Figure 19 shows the CERC formula predictions ploted against field datacompiled by Davies (1984).Equation 8 gives 83% higher volume transport rates than its predecessor Equation 5. The reasons forthis upward revision on the dimensional coefficient of the CERC formula are given by Galvin and Vitale(1976). The major change is the deletion of all laboratory data from the curve fiting. Thus, Equation 8 resultsfrom a plot of only the available set of field data, e.i. Wats (1953), Caldwell (1956) and Komar and Inman(1970), and is shown in Figure 19, taken from U.S. Army Corps of Engineers (1977). A review of this database is given in Greer and Madsen (1978), who critically question their quality and conclude that Equation8 should be used with caution, only as an order of magnitude estimate for the littoral transport rates. However,the CERC formula continues to have the preference of researchers in the USA (Bodge, 1991 ) and wasincluded in the CERC's model for shoreline evolution GENESIS (Gravens, 1 991).Queen's Formula for Littoral TransportKamphuis and Sayao (1982) have shown that there is a strong dependence of the dimensionlesslitoral transport rate on the surf similarity parameter, as may be seen on Figure 20, for model data of mediumand fine sands. The following expression was derived:Qs = b (10)where is the dimensionless sediment transport rate, is the suspended load coefficient andQsb is the surf similarity parameter (or Iribarren number; Batjjes, 1974) defined as:m= --------- (11)H/L 0The surf similarity parameter in the breaking zone (4b) is calculated with Hb as the wave heightvalue. This parameter gives an indication of the rate of energy dissipation in the surf zone. The breaker typeand other surf zone phenomena are also related to 4 as shown in Figure 21.

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 134Equation 10 may be written as follows:s(1 - p ) Q 's_____________ = (12)b1 H 3 b- ----- sin 2 b2 Twheresis the sediment density, Q' is the volumetric transport rate.sFigure 22 shows a plot of 1c versus the relative grain size parameter, in order to investigate on theform of the functional relationship of Equation 10. Nairn (1985) has demonstrated in model experiments withsacrificial sand islands that an H/D value of about 300 is a limit for inception of suspended load. For valuesof H/D less than 300, larger grain sizes display greater erosion rates. Consequently, laboratory data pointswith H/D less than 300 were omitted from the analysis (Sayao et al., 1985).An expression was determined for available laboratory data with H/D greater than 300 and for fielddata points compiled by Davies (1984) as follows (see Figure 22):H b= 0.002 (---) (13)D 50where D is the median grain size of the beach sediment. Equation 13 was used to calculate sediment50transport rates at Pointe-Sapin, see Kamphuis et al., (1986), with good results. Using Equations 11, 12 and13 comes:m g H b3.5-4Q s' = 4 x10 -------------- . ------------ . sin 2(14)Ds 50( 1 - p ) ---bAlso, Sayao and Chow (1992) have further enhanced Queen's formula (Equation 14) to include aterm first proposed by Ozasa and Brampton (1980) to take into account the iongshore variation of wavebreaking heights.Steady Flow Modification ApproachMost formulas for sediment transport in unidirectional steady flow can be expressed by using theEinstein (1950) dimensionless parameters ¢ and Nr, as follows:= f( ) (15)with the parameterrelated to the sediment transport itself:q s1/2= ------------( D)s

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 135andrelated to the flow characteristics:1 D s= ---- = --------Fv2* *Here q s is the weight sediment transport rate per unit width, F * is the mobility number (or Shieldsparameter), s is the underwater unit weight of sediment, ( s - )g, is the fluid density, s the sedimentdensity and v * is the shear velocity. Equation 13 is known as the ' - 'curve' and may be found in mostsediment transport textbooks, e.g. Yalin (1977). A modification of Equation 15 to enable its use for twodimensional oscillatory flow, i.e. coastal sediment transport, has been the subject of many research efforts(Madsen and Grant, 1976; Swart, 1976; Bijker, 1971).Owing to the lack of any comprehensive field data on littoral transport rate, van de Graaff and vanOvereem (1979) decided to compare some of the more detailed formulas with the CERC formula for littoraltransport. As a result of this comparison the Bijker formula appeared to be better than other steady flowmodification formulas, but it may be argued that the CERC formula cannot be used as a standard in such acomparison.Swart and Fleming (1980) have made an attempt at comparing the mean sediment transport rateobtained by using six predictors, including the CERC formula, with a prototype situation, a high energy beachlocated north of Cape Town, South Africa, where the transport rates were inferred from quarterly bathymetricsurveys over 2 years. The result showed good agreement between prototype data and mean predicted ratesbut no appraisal of each individual formula was made.Cross-Shore Transport ModelsBeach profile evolution and cross-shore sediment transport have in the past been neglected incoastal studies and design. Only recently the relevance of cross-shore transport has been identified. However,existing prediction methods have not yet been validated. In fact, Seymour and King (1982) and Seymour andCastel (1988) have compared several first generation (empirical, based primarily on laboratory data) modelsto field data collected in both USA coasts, during the Nearshore Sediment Transport Study, with very poorresults.As far as cross-shore transport is concerned, Seymour and Castel (1988) discuss that only the Swartprofile model (Swart, 1976) showed "interesting skill in predicting unbarred type profile sets", however itfailed to predict the evolution of a profile data set dominated by longshore bar movements. Also, Seymourand Castel (1988) concluded that "a realistic model for cross-shore transport, involving the necessary physics,appears to be well beyond the present state of the art".The CERC experience in two-dimensional profile modelling shows that the predictor developed byKriebel (1990; see Figures 15 and 16), based on a 'Dean Profile', the exponential form for the equilibriumbeach profile put forth by Dean (1977; 1990), may well suit their needs along the Atlantic Coast. However,the Kriebel profile model cannot handle longshore bar evolution. Recent work by Larson et al., (1990) andKriebel et al., (1991) has included these processes in the new versions of the model.Presently, research efforts in Europe have yielded new second generation profile models, where thephysics of cross-shore processes are taken into account (see Stive, 1986; Nairn, 1988; Hedegaard et al., 1991;Southgate, 1991; de Vriend, 1991). Profile changes and cross-shore transport may now be modelled with amodel that can predict the evolution of barred beaches, which is the case for most beaches in the Great Lakes.This cross-shore transport numerical model provides a description of coastal processes in both the longshoreand cross-shore directions for random waves and currents such as tides on a sandy beach profile. The modelhas four predictive phases including (Nairn, 1988 and Southgate, 1988):i) wave height transformation,ii) hydrodynamics,

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 136iii)sediment transport in the cross-shore and longshore directions, and iv) cross-shore profileevaluation.Beach Evolution ModelsFurther to the calculation of sediment transport in the cross-shore and longshore directions, beachevolution analyses may be carried out, such as:A beach plan evolution model may be used to access the impact of littoral barriers onsediment processes along the shoreline.The effects of natural beach areas on the sediment regime may also be assessed bycomparison of supply, potential rates and predictions of beach evolution with time.In general, the following types of numerical models of beach evolution exist:a '1 -line' type model, which takes into account the evolution of one contour only, typicallythe shoreline; with or without seawall and revetments on the beach;a 'n-lines' type model, which takes into account the evolution of several contours; anda cross-shore profile evolution model, a 2DV nearshore model (2-dimensional in the verticaland cross-shore horizontal dimensions).The 1 -l i ne type beach model assumes that the beach profi le always remai ns in equi librium andthat the beach profile changes from the shoreline to the depth of closure occur with parallel slopes. Hence,only one contour is sufficient to describe the change of shoreline position from initial.These numerical models were developed based on the work of Pelnard-Considere (1954). Severalapplications are available in literature, including Ozasa and Brampton (1980), Komar (1984), Kraus andHarikai (1983) and Hanson and Kraus (1989).The 'n-lines' model was originally developed by Perlin and Dean (1983) and has been used by CERCand others for prediction of short term shoreline changes (Figure 23). The model consists of a representationof the nearshore zone, with the bathymetric contours represented by 'n' lines, each one of a specified depth.Three basic equations are used to simulate two-dimensional sediment transport rate and bathymetric changes;the equation of continuity of sand; a longshore transport predictor, and a cross-shore sediment transportequation. The bulk longshore sediment transport rate is determined with the CERC formula (U.S. Army Corpsof Engineers, 1984), coupled with Fulford (1 983) distribution in the cross-shore direction. The cross-shoresediment transport rate is determined by using an activity factor as suggested by Bakker (1968) and Dean's(1977) equilibrium profile shape. A detailed description is found in Perlin and Dean (1983).The 'n-lines model may be modified according to the site-specific modelling situation. For instance,Johnson and Kamphuis (1988) have used an 'n-lines' model to predict morphological changes in large sandislands; Sayao and Chow (1992) have used a grided wave transformation model based on Resio's (1988)work, to better predict waves in the lee of offshore breakwaters.Another type of evolution models is the 2DV nearshore profile model, that include wavetransformation procedures, tidal and wave-induced currents, cross-shore undertow velocities, crossshore andlongshore sediment transport rates to compute beach profile changes, assuming straight shoreline with parallelcontours (Nairn, 1988; 1991; Southgate, 1988; 1991). Presently, this modelling work is being extended to3-dimensional shoreline situations.Recently CERC has developed a '1 -line' shoreline change model called GENESIS (generalizedmodel for simulating shoreline changes; see Hanson and Kraus,1989 and Gravens,1991). GENESIS allowssimulations of shoreline changes occurring over a period of months to years as caused primarily by the actionof breaking waves. The project horizontal length scale typically varies from one up to tens of kilometres. Themodel is generalized in the sense that the it can be used to simulate shoreline change under a wide variety ofuser specified beach structure configurations. In addition, the input wave conditions can be entered either byassuming parallel bottom contours (Snell's Law), or through interaction with a more rigorous wave refractionmodel (see Figure 24).

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 137GENESIS is based on the one-line theory of beach change (Pelnard-Considere, 1954). The sameconcept has been used in a number of previous studies (e.g., Price et al., 1973, Perlin 1979, LeMehaute andSoldate, 1 980). In particular, Hanson et al., (1988; 1989), Kraus et al., (1988), and Hanson and Kraus (1989)present applications of the GENESIS model employed as an engineering tool for making shoreline changeforecasts for real (prototype) beaches (see Figure 25).These models proved to be powerful tools for the prediction of short term and long term beachevolution at coastal sites. The results of the simulations may be used for conceptual planning of coastalprojects, by assessing the impact of structures on shoreline changes, as well as enabling the development ofmitigation measures.The typical phases of a modelling analysis of existing coastal processes are as follows:Short Term Modelling AnalysisAt this phase of a modelling analysis, an understanding of the existing coastal processes is developed,considering both detailed longshore and cross-shore sediment transport patterns. Selected storms, selectedextreme events, and/or a selected 1 year time series may be used to investigate typical storm and recoveryperiods. This exercise would elucidate the role of cross-shore transport on the littoral processes at the siteunder consideration, as well as, the distribution of longshore transport across the beach profile. Also,importantly, gradients of longshore transport rate must be investigated for they may play a role in littoralprocesses along curved or partially, protected beaches.Long Term Modelling AnalysisIn this phase of the studies, the deep water wave hindcast data (MNR, 1988a; 1988b; 1988c) maybe used to investigate shoreline changes. The models could be applied to long term data in a chronologicalformat to establish yearly averages of net and gross sediment transport rates, as well as shoreline andnearshore changes. In this phase of the work only gross shoreline changes will be considered and theirinterpretation will be based on the detailed understanding developed during the short term investigation.Conceptual Shoreline <strong>Planning</strong>In this phase, prediction of shoreline changes may be carried out for master planning purposes.Future shoreline changes are modelled, for periods of 5 years, 10 years or 25 years. An importantconsideration here is the effect of wave variability on transport rates. This aspect was considered by LeMehaute et al., (1983), as well as in past coastal studies such as the ones presented in Kraus and Harikai (1983) and Brampton and Motyka (1 987).

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 138ANNEX IREFERENCESBAGNOLD, R.A. 1963. Mechanics of marine sedimentation in the sea: ideas and observations.Vol. 3, Interscience, N.Y.BAILARD, J.A. 1981. An energetics total load sediment transport model for a plane sloping beach. Journalof Geophysics Research, Vol. 86, No. C11, pp. 10938 - 10954.BAKKER, W.T. 1968. The dynamics of a coast with a groyne system. Proc. of the 11 th CoastalEngineering Conference, ASCE, pp 492 - 517.BASCOM, W.J. 1980. Waves and beaches. 2nd edition, Anchor Books, N.Y., 366 p.BATTJES, J.A. 1974. Surf similarity. Proc. 14th Coastal Engineering Conference, ASCE,Copenhagen, Denmark, pp. 466-477.BIJKER, E.W. 1971. Longshore transport computation. Journal of the Waterway, Port, Coastal and OceanDivision, ASCE, Vol. 97. WW4, pp. 687-701, November.BIRKEMEIER, W.A. 1991. Field data for cross-shore transport models. Unpublished notes,<strong>Workshop</strong> on Development and Application of Cross-shore Sediment Transport and Beach ProfileChange Models, CERC.BODGE, K.R. and KRAUS, N.C. 1991. Critical examination of longshore transport rate magnitude. Proc.Coastal Sediments '91, Seattle, Washington, ASCE, Vol. l, pp.139-155.BOWEN, A.J. 1980. Short course lecture notes basic nearshore processes. April 12, 1980,Burlington, Ontario, ACROSES, NRCC, Ottawa.BOYD, G.L. 1981. Great Lakes erosion monitoring programme. Final Report, Ocean Science andSurveys, Bayfield Lab. for Marine Science and Surveys, Burlington Ontario. Unpublished Manuscript, 220pp.BRAMPTON, A.H. and MOTYKA, J.M. 1987. Recent examples of mathematical models of U.K. beaches.Proc. Coastal Sediments '87, New Orleans, Louisiana, ASCE, May, pp.515 - 530.BRUNO, R.O., DEAN, R.G., GABLE, C.G. and WALTON, T.L. 1981. Longshore sand transportstudy at Channel Island Harbour. California. Technical Paper No. 81-2, CERC, U.S. Army Corpsof Engineers, April.CALDWELL, J.M. 1956. Wave action and sand movement near Anaheim Bay, California.Technical Memorandum No. 68, Beach Erosion Board, U.S. Army Corps of Engineers.DAS, M.M. 1971. Longshore sediment transport rates: a compilation of data. Miscellaneous Paper No.1-71, CERC, U.S. Army Corps of Engineers, September.DAVIES, M.H. 1984. Littoral transport rate prediction. M.Sc. Thesis, Department of CivilEngineering, Queen's University, Kingston, Canada.DEAN, R.G. 1990. Equilibrium beach profiles: characteristics and applications. Report UFL/COLF 90/001,University of Florida, Gainesville, Florida, 70 pp.DEAN, R.G. 1977. Equilibrium beach profiles: U.S. Atlantic and Gulf Coasts. Tech. Report No.12, University of Delaware, Newark.DEAN, R.G., 1973. Heuristic models of sand transport in the surf zone. Proc. 1st AustralianConference on Coastal Engineering, Sydney, Australia, p. 208 - 214.DEVRIEND, H.J. 1991. G-6 Coastal morphodynamics. Proc. Coastal Sediments '91, Seattle,Washington, ASCE, Vol. l, pp. 356-370.EINSTEIN, H.A. 1950. The bed-load function for sediment transportation in open channel flows. U.S.Department of Agriculture, Soil Conservation Service, Technical Bulletin Bo. 1026.EINSTEIN, H.A. 1948. Movement of beach sand by water waves. Transactions of the AmericanGeophysical Union, Vol. 29, No. 5, pp. 653 655, October. 2lFULFORD, E. 1983. Sediment transport distribution across the surf zone. M.Sc. Thesis presented to theUniversity of Delaware, Newark, USA.GALVIN, C.J. and VITALE, P. 1 976. Longshore transport prediction - SPM 1973 Equation. Proc. Ofthe 15th International Conference on Coastal Engineering, Honolulu, Hawaii, ASCE, Vol. II, pp.1133-1148.GREER, M.N. and MADSEN, O.S. 1978. Longshore sediment transport data: a review. Proc. of the 16thInternational Conference on Coastal Engineering, Hamburg, Germany, ASCE, Vol. II, pp.1563-1576.GRAVENS, M.B. 1991. Development of an input data set for shoreline change modelling. Proc.Coastal Sediments '91, Seattle, Washington, ASCE, Vol. ll, pp. 1800-1813.HANSON, H. and KRAUS, N.C. 1989. GENESIS: generalized model for simulating shoreline

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 139change. Technical Report CERC-89-19, Report 1, Department of the Army, U.S. Army Corpsof Engineers, Washington, DC 20314-1000.HANSON, H., KRAUS, N.C., and NAKASHIMA, L.D. 1989. Shoreline change behind transmissivedetached breakwaters. Proc. Coastal Zone'89, ASCE, pp. 568-582.HANSON, H., GRAVENS, M.B and KRAUS, N.C. 1988. Prototype applications of a generalizedshoreline change numerical model. Proc. 21st International Conference on CoastalEngineering, ASCE, pp. 1265-1279.HARAS, W.S. and TSUI, K.K. 1976. Canada/Ontario Great Lakes shore damages survey, Coastal ZoneAtlas. Environment Canada and the Ontario Ministry of Natural Resources.HEDEGAARD, I.B., DEIGAARD, R. and FREDSOE, J. 1991. Onshore/offshore sediment transport andmorphological modelling of coastal profiles. Proc. Coastal Sediments '91, Seattle, Washington, ASCE, Vol.I, pp. 643-657.HORIKAWA, K. 1988. Nearshore dynamics and coastal processes. University of Tokyo Press.HOTTA, S. 1980. Wave height distribution around permeable breakwaters. Proc. 17th Int.Conference on Coastal Engrg, ASCE, pp. 221 - 240.HOTTA, S. and MIZUGUCHI, M. 1986. Wave statistics in the surfzone Abstract, 20thInternational Conference on Coastal Engineering, ASCE.IBBOTT, P. and WHITTINGTON, M. 1 991. Valuation of shoreline expenditure in Canada - 1988.Executive summary. ACOS Bulletin, Vol. 5, No.1, NRCC, Spring, 05-11.INMAN, D.L. and BAGNOLD, R.A. 1963. Beach and nearshore processes part 11: littoral processes.Contribution to 'The Sea' Vol.3, General Editor M.N. Hill, pp. 529-553, John Willey & Sons.IWAGAKI, Y. and NODA, H. 1962. Laboratory study of scale effects in two-dimensional beachprofiles. Proceedings of the 8'h Coastal Engineering Conference, Mexico City, Mexico,Council of Wave Research, Chapter 14, pp. 194-210.JOHNSON, H.K. and KAMPHUIS, J.W. 1988. N-line morphology model foa a large initiallyconical sand island. Proc. IAHR Symposium on Mathematical Modelli ng of SedimentTransport in the Coastal Zone, Copenhagen, Denmark, pp.275-289.KAMPHUIS, J.W. 1990a. Improving shore protection design. Proc. Canadian Journal of CivilEngineering, NRCC, April, Vol. 17, No. 2, pp. 142-147.KAMPHUIS, J.W. 1990b. Littoral transport rate. Proc. 22nd International Conference on CoastalEngineering, Delft, The Netherlands, ASCE, Vol. 3, pp. 2402-2415.KAMPHUIS, J.W. 1986. Erosion cohesive bluffs, a model and formula. Proc. Symposium onCohesive Shores, Burlington, Ontario, pp. 226-245.KAMPHUIS, J.W., DAVIES, M.D., NAIRN, R.B. and SAYAO, O.J. 1986. Calculation of littoral sandtransport rate. Coastal Engineering, Elsevier, Vol. l0, pp. I - 21KAMPHUIS, J.W. and SAYAO, O.J. 1982. Model tests on littoral sand transport rates. Proc.18thInternational Conference on Coastal Engineering, ASCE, Cape Towm, South Africa, Vol. ll, pp.1305-1325.KEMP, P. 1962. A model study of the behaviour of beaches and groins. Proceedings of the Institution ofCivil Engineers, London, Vol. 22, pp.191-210.KEMP, P. 1960. The relationship between wave action and beach profile characteristics. Proc. 7th CoastalEngineering Conference, The Hague, The Netherlands, ASCE, pp. 262-276.KEMP, P. and PLINSTON, D.T. 1968. Beaches produced by waves of low phase difference. Journal ofthe Hydraulics Division, ASCE, Vol.94, No.HY5, pp.1183-1195.KING, C.A.M. 1972. Beaches and coasts. 2nd. edition, Edward Arnold.KOHLER, R.R. and GALVIN, C.J. 1973. Berm-bar criterion. Unpublished CERC Laboratory Report,August, 70 p.KOMAR, P.D. 1984. CRC Handbook of coastal processes and erosion. CERC Press, Inc. Boca Raton,Florida.KOMAR, P.D. 1976. Beaches processes and sedimentation. Prentice-Hall, Inc. 425 pp.KOMAR, P.D. and INMAN, D.L. 1970. Longshore sand transport on beaches. Journal of GeophysicalResearch, Vol. 75, No. 30, pp. 5514-5527.KRAUS, N.C. 1991. Engineering needs and applications of beach profile models. Unpublished notes,<strong>Workshop</strong> on Development and Application of Cross-shore Sediment Transport and Beach ProfileChange Models, CERC.KRAUS, N.C. 1989. Beach change modelling on the coastal planning processes. Proc. Coastal Zone '89,ASCE, pp. 553-567.KRAUS, N.C. LARSON, M. and KRIEBEL, D.L. 1991. Evaluation of beach erosion and accretionpredictors. Proc. Coastal Sediments '91, Seattle, Washington, ASCE, Vol. l, pp. 572-587.

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 140KRAUS, N.C., HANSON, H. and LARSON, M. 1988. Threshold for longshore sand transport andapplication to a shoreline change simulation model. Proc. IAHR Symposium on MathematicalModelling of Sediment Transport in the Coastal Zone, Copenhagen, Denmark, pp 117-126.KRAUS, N.C. and HARIKAI, S. 1983. Numerical model of the shoreline change at Oarai Beach. CoastalEngineering, Elsevier, Vol. 7, pp.1 - 28.KRIEBEL, D.L. 1990. Advances in numerical modelling of dune erosion. pp.2304-2317. Proc. 22ndInternational Conference on coastal Engineering, Delft, The Netherlands, ASCE, Vol 3, pp. 2304-2317.KRIEBEL, D.L., KRAUS, N.C. and LARSON, M. 1991. Engineering methods for predicting beach profileresponse. Proc. Coastal Sediments '91, Seattle, Washington, ASCE, Vol. l, pp. 557571. LARSON, M.,KRAUS, N.C. and BYRNES, M.R. 1990. SBEACH: numerical model for simulating storm-inducedbeach change. Technical Report, CERC-89-9, Report 2, Department of the Army, U.S. Army Corps ofEngineers, Washington, DC 20314-1000.LAW, M.N., SAUNDERS, K.E., COLEMAN, D.E., FISHER, J.D., VAN WYNGAARDEN, R., BOYD,G.L. and STEWART, C.J. 1991. Using GIS to monitor and predict long-term Great Lakes shoreline erosion.Proc. The Canadian Conference on GIS-91, March, Ottawa, Energy \, Mines and Resources Canada, pp.372-386.LEMEHAUTE, B., WANG, J.D. and LU, C.C. 1983. Wave data discretisation for shoreline processes.Proc.Journal of Waterway, Ports, Coastal and Ocean Engineering Division, ASCE, 109, WW1.LEMEHAUTE, B. and SOLDATE, M. 1980. A numerical model for predicting shoreline changesU.S. Army Corps of Engineers, CERC, Misc. Report No. 80-6, July.LONGUET-HIGGINS, M.S. 1972. Recent progress in the study of longshore currents. In: 'Waves onBeaches and Resulting Sediment Transport', ed. R.E. Meyer, Academic Press, N.Y.MADSEN, O.S and GRANT, W.D. 1976. Quantitative description of sediment transport by waves.Proc.15thInternational Conference on Coastal Engineering, Honolulu, Hawaii, ASCE, Vol. II, pp. 1093-1112.MOTTA, V.F. 1964. A questao da correlacao entre esbeltez das ondas do mar e o tipo de perfilde equilfbrio formado em praia sem mare por ondas monocromaticas. Anais do 1O.Congresso Latino-americano de Hidraulica, Porto Alegre, Brasil, IAHR, Vol.2, pp.1-47.MNR, 1988a. Wave hindcast database for Lake Ontario and Lake Superior. Final Report, Ontario Ministryof Natural Resources, Conservation Authorities and Water Management Branch, March.MNR, 1988b. Wave hindcast database for Lake Erie and Lake St. Clair. Final Report, OntarioMinistry of Natural Resources, Conservation Authorities and Water Management Branch, March.MNR,1988c. Wave hindcast database for Ontario's Great Lakes - Lake Huron/Georgian Bay. Final Report,Ontario Ministry of Natural Resources, Conservation Authorities and WaterManagement Branch, March.MNR, 1988d. Littoral cell definition and sediment budget for Ontario's Great Lakes. Final Report, OntarioMinistry of Natural Resources, Conservation Authorities and Water Management Branch, March.NAIRN, R.B. 1991. Problems associated with deterministic modelling of extreme beach erosionevents. Proc. Coastal Sediments '91, Seattle, Washington, ASCE, Vol I, pp. 588-602.NAIRN, R.B. 1988. Prediction of wave height and mean return flow in cross-shore sedimenttransport modelling. Proc. IAHR Symposium on Mathematical Modelling of SedimentTransport in the Coastal Zone, Copenhagen, pp. 193 - 202.NAIRN, R.B. 1985. Scale series approach to coastal mobile bed modelling. M.Sc. Thesis,Department of Civil Engineering, Queen's University, Kingston, Canada.NIELSEN, P. 1979. Some basic concepts of wave sediment transport. Inst. of Hydrodynamics andHydraulic Engineering (ISVA). Series Paper 20. Tech. University of Denmark, 160 pp.OZASA, H. and BRAMPTON, A.H. 1980. Mathematical modelling of beaches backed byseawalls. Coastal Engineering, Vol. 4, No.1, pp. 47-63.PELNARD-CONSIDERE, 1954. Essay on the theory of the evolution of the form of beaches andbars. Quatroeme de l'Hydraulique, Paris, Question 3, Les Energies de la Mer.PERLIN, M. 1979. Predicting beach planforms in the lee of a breakwater. Proc. Coastal Structures '79,ASCE, pp. 792-808.PERLIN, M. and DEAN, R.G. 1983. A numerical model to simulate sediment transport in thevicinity of coastal structures. MR83-10, U.S. Army Corps of Engineers, Coastal EngineeringResearch Centre, Ft. Belvoir, Va.PRICE, W.A., TOMLINSON, K.W. and WlLLiS, D.H. 1973. Predicting changes in the plan shapeof beaches. Proc. 13th Internatinal Conference on Coastal Engineering, Vancouver, B.C., ASCE,pp. 1321 -1329.RESIO, D.T. 1988. A steady-state wave model for coastal applications. Proc. 21st InternationalConference on Coastal Engineering, ASCE, Malaga, Spain, pp. 929-940

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 141RUKAVINA, N.A. 1976. Nearshore sediments of Lake Ontario and Erie. Geoscience Canada, V.3(3),pp. 185-190SAVAGE, R.P.1962. Laboratory determination of littoral transport rates. Journal of the Waterways, Port,Coastal and Ocean Division, ASCE, No. WW2, pp. 69-92.SAYAO, O.J. 1982. Beach profile and littoral sand transport. Ph.D. Thesis, Department of civilEngineering, Queen's University at Kingston, Canada.SAYAO, O.J. and CHOW, K.C.A. 1992. Application of a beach plan evolution model in Sergipe, Brazil.Proc. Coastal Engineering Practice '92, ASCE, to be published.SAYAO, O.J. and GRAHAM, J.E. 1991. On the prediction of beach profiles. ACOS Bulletin, Vol. 5,No.1, NRCC, Spring, 14-19.SAYAO, O.J., HODGINS, D.O. and MORGAN, P. 1987. Sediment transport predictions off Sable Island,Canada. Proc. Canadian Coastal Conference, Quebec, NRC/ACOS, July, pp.99-113.SAYAO, O.J., NAIRN, R.B. and KAMPHUIS, J.W. 1985. Dimensional analysis of littoral transport.Proceeding, Canadian Coastal Conference, St. John's, Newfoundland, Associate Committee onShorelines, National Research Council Canada,pp.241-255.SAYAO, O.J. and KAMPHUIS, J.W. 1983. Littoral sand transport: review of the state of the art. C.E.Research, Report No. 78, January, Dept. of Civil Engineering, Queen's University, Kingston,Ontario.SAYAO, O.J. and KAMPHUIS, J.W. 1982. Wave action on beaches. C.E. Research, Report No. 77,November, Department of Civil Engineering, Queen's University, Kingston, Ontario.SEYMOUR, R.J.andCASTEL, D. 1988. Validationofcross-shoretransportformulations. Proc.21stInternational Conference on Coastal Engineering, Malaga, Spain, ASCE,2, pp.1676 - 1688.SEYMOUR, R.J. and KING JR., D.B. 1982. Field comparisons of cross-shore transport models. Journalof Waterway, Port, Coastal and Ocean Division, ASCE, 108 (WW2), pp. 163 -179.SEYMOUR, R.J. and GABLE, C.G. 1980. Nearshore sediment transport study experiments. Proc. Ofthe 17th International Conference on Coastal Engineering, Sydney, Australia, ASCE, Vol. II,pp.1402-1415.SEYMOUR, R.J. and DUANE, D.B. 1978. The nearshore sediment transport study. Proc. of the 16thInternational Conference on Coastal Engineering, Hamburg, Germany, ASCE, Vol. ll, pp.1555-1562.SHEPARD, F.P. 1954. Nomenclature based on sand-silt-clay ratios. J. Sed. Petrol., Vol. 24, pp. 151-158.SILVESTER, 1974. Coastal Engineering, 2. Developments in Geotechnical Engineering, Vol. 4B, ElsevierScientific Publishing Company, 338p.SITARZ, J.A. 1963. Contribution a ltetude de ltevolution des a partir de la connaissance des profilsd'equilibre. Travaux du Centre de Recherches et d'Edudes Oceanographiques, Vol.5, Paris.SMITH, G.M. and SAYAO, O.J. 1989. Definition of littoral cells for Ontario's Great Lakes shorelines. Proc.Coastal Zone '89, Charleston, South Carolina, ASCE, pp. 3771-3784.SOUTHGATE, H.N. 1988. The nearshore profile model: a computational model of wave and currentinteraction in nearshore regions. Hydraulics Research Ltd., Report SR 157, 57 ppSOUTHGATE, H.N. 1991. Beach profile modelling: flume data comparisons and sensitivity tests. Proc.Cosatal Sediments '91, Seattle, Washington, ASCE, Vol. ll, pp. 1829-1841.STIVE, M.J.F. 1991. Cross-shore transport modelling on different scales. Unpublished notes,<strong>Workshop</strong> on Development and Application of Cross-shore Sediment Transport and Beach Profile ChangeModels, CERC.SUNAMURA, T. 1989. Sandy beach geomorphology elucidated by laboratory modelling. Applicationsin Coastal Modelling, Chapter 6, V.C. Lakham and A.S. Trenhaile (Editors), Elsevier OceanographySeries, 49, Elsevier, pp.159-213.SUNAMURA, T. 1 984. Quantitative predictions of beach-face slopes. Geol. Soc. America Builetin, Vol.95,pp.242-245.SUNAMURA, T. and HORIKAWA, K. 1974. Two dimensional beach transformation due to waves.Proceedings of the 14'h Coastal Engineering Conference, Copenhagen, Denmark, ASCE, Vol.ll,pp.920-938.SWART, D.H. 1976. Predictive equations regarding coastal transport. Proc. 15th InternationalConference on Coastal Engineering, Honolulu, Hawaii, July, ASCE, Vol.ll, pp.1113 - 1132.SWART, D.H. and FLEMING, C.A. 1980. Longshore water and sediment movement. Proc. 1 7thInternational Conference on Coastal Engineering, Sydney, Australia, ASCE, II, pp.1275-1294.TAKEDA, I. and SUNAMURA, T. 1982. Formation and height of berms. Trans. Japan.Geomorphological Union 3, pp.145-157 (in Japanese, with English abstract).

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 142THORNTON, E.B. and GUZA, R.T. 1986. Surfzone longshore currents and random waves: field dataand models. Journal Phys. Oceanography, Vol. 1 6, pp. 1165-1178.U.S. ARMY CORPS OF ENGINEERS, 1984. Shore Protection Manual. 4th edition, CoastalEngineering Research Centre, Washington.U.S. ARMY CORPS OF ENGINEERS, 1 977. Shore Protection Manual. 3rd Edition, CoastalEngineering Research Center. Washington.VAN DE GRAFF, J. 1 980. Closure discussion of evaluation of sediment transport formulae in coastalengineering practice. Coastal Engineering, Vol. 4, pp. 180-181, Elsevier.VAN DE GRAFF, J. and VAN OVEREEN, J. 1979. Evaluation of sediment transport formulae in coastalengineering practice. Coastal Engineering, Vol. 3, pp. 1-32, Elsevier.VITALE, P. 1 980. A guide for estimating longshore transport rate using four SPM methods. Coastalengineering Technical Aid No. 80-6, CERC, U.S. Army Corps of Engineers, April.WATTS. G.M. 1953. A study of sand movement at South Lake Worth inlet, Florida. Beach Erosion Board,Technical Memorandum No. 42, U.S. Army corps of Engineers.WHITE, W.R., MILLI, H. and CRABBE, A.D. 1975. Sediment transport theories: a review. Proc. ofthe Institution of Civil Engineers, London, Part 2, Vol. 59, pp. 265-292.WIEGEL, R.L. 1964. Oceanographical Engineering. Prentice-Hall Inc.WlLLIS, D.H. 1987. The canadian coastal sediment study: an overview. Proc. Coastal Sediments '87,New Orleans,Louisiana, ASCE, Vol. l, pp. 682-693.WILLIS, D.H. 1979. Sediment load under waves and currents. National Research Council of Canada,DME/NAE Quaterly Bulletin No. 1979(3), Ottawa.YALIN, M.S. 1977. Mechanics of sediment transport. 2nd Edition, Pergamon Press.ZENKOVICH V ' 1967 Processes of coastal development. Oliver and Boyd, Edinburgh

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<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 166IX.REGIONAL. ASPECTS OF COASTAL EROSION IN WES TAFRICA - THE CASE OF THE BIGHT OF BENINby J WELLENS-MENSAHABSTRACTThe paper gives a brief general description of the Bight of Benin which forms part of the West African Coast.It examines the general coastal conditions and the causes of erosion in the Bight It then discusses coastalprotection measures in the various countries in the Bight and finally discusses the future direction of coastalerosion control in the Bight of Benin .1. INTRODUCTIONThe information contained in this paper has been drawn mainly from the following publications:(i) Coastal Erosion in the Bight of Benin. Report on Expert Findings. E E.C. (1989).(ii) Coastal Erosion in West and Central Africa. <strong>UNEP</strong> (1985).(iii) Coastal Erosion in Ghana. Situation Report and Action Programme. Team of Consultants onCoastal Erosion Report to the government of Ghana (1986)Those three reports have in turn drawn heavily on information available in technical reports on coastal erosionin the West African Sub-region. These three reports have thus become compendia of coastal erosioninformation in the sub-region.2. GENERAL DESCRIPTION OF THE BIGHT OF BENINThe Bight of Benin is part of the Coast of Guinea. The coasts that comprise the Bight are those ofCote D' Ivoire Ghana, Togo, Benin, Nigeria and part of the coast of Cameroon. More specifically these coastswith distinct geo-morphologicl characteristics are (Fig.1):(i)(ii)(iii)the coast from Cape Palmas in La Cote d' Ivoire to Cape Three Points in GChancthe coast form Cape Three Points to the Western extremity of the Niger Delta in Nigeriathe Niger Delta up to the promontory of Mount Cameroon.The entire length of the Bight measures about 2000 km end lies between longitudes 8 W and 9 Eclose to latitude 5 N. The notable rivers discharging into the ocean in the Bight are River Niger inNNigeriaand River Volta in Ghana. Other smaller rivers discharging into the ocean are the Pra ln Ghana; theSassandra, Bandama and Komoe in Cote d' Ivoire; the Mono and Oueme in Benin and the Cross River inNigeria. The Niger which is the largest river in the Bight splits into a pronounced delta around longitude 6 E,the Volta forms a smaller delta around 1 E longitude.The coastal area in the Bight is generally low-lying with the lOOm contouring occurring at a distanceof 25 km to 100 km inland . It is characterized by steep coasts with small bays and narrow sandy beachesbetween Cape Palmas and Cape Three Points and low beach ridges, marshes and lagoons for the rest of thecoast.

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<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 168The continental shelf in the Bight is generally narrow with widths of:* 20 to 25 km along the coast of Cote d'Ivoire, Togo, Benin and West Nigeria.* 20 to 80 km between Cape Three Points and the Volta Delta, and* 50 to 65 km in front of the Niger DeltaThe Continental Slope in generally steep. Distinct submarine canyons exist off the Canal de vridi in Coted'Ivoire, Western Nigeria, the Volta Delta, the western coast of the Niger Delta and off the Calabar Estuary.3. CLIMATEThe climate in the Bight is tropical and is characterized by varying amounts and distribution ofrainfall. The western part of Ghana, Cote d'Ivoire as well as the coast to the east of Cotonou in Benin recordrainfall amounts above 1500 mm in a year The vegetation in these areas is tropical rain forest. In responseto the movement of the Inter Tropical Convergence Zone (ITCZ), two rainfall maxima occur in May - Juneand October - November. The coast between Takoradi in Ghana and Cotonou in Benin receives much lessrainfall (about 100 mm,/year), and is relatively dry with a Savanna type of Vegetation. TemperatureVariation is small. The average daily maxima varies between 27 - 29 C in August - September and 31-33 C in February - March The average daily minima are from 21 - 22 C in August to 23 - 24 C in March.The Prevailing winds are the south-westerly monsoons, modified by land and Sea breezes in thecoastal area Wind speeds vary between 0 5 - 2.5 m/s at night and 2 - 6 m/s during the day Storms are rare.However, line squalls with heavy rains and strong winds of short duration occur occasionally .Between December to February the hot dry Harmattan winds are felt. Evaporation and evapo-transpirationrates are higher especially in the coast between Takoradi in Ghana and Cotonou in Benin during the dryseason. The effect of the high evaporation rates in the dry season is very much reflected in the state of lagoonsand marshes, which record very low depths or completely dry out.4. HYDROLOGYThe large rivers discharging into the ocean, notably the Niger and the Volta, peak around August -October. Low discharges are recorded for the rest of the year. Smaller Coastal rivers and streams flow onlyin the wet season. Relatively little is known about the sediment discharges of the rivers flowing into the oceanin the Bight. Based on information on a few local rivers and other areas with similar conditions, an estimateof sediment yields of 30 to 80 tons/km2 per year has been calculated. The estimated sediment loads of themain rivers and small coastal catchments is 92 .6 Million tons per year. The percentage of sand in the totalload has been estimated to be 10 to 15%. The corresponding volume of sand in the total load has beenestimated to be 7.14 million m3/year.5. OCEANOLOGYThe Bight of Benin faces the South Atlantic Ocean. The continental shelf in this region is generallynarrow with no offshore islands to protect the coast against tides, currents and waves.The tide is semi-diurnal and occurs almost synchronous in the Bight with an average range of about onemeter. The tidal range is however higher towards the for east of the Bight. The coastal currents caused bythese tides are generally weak.The Guinea current which is experienced in the Bight flows offshore from west to east as acontinuation of the Equatorial Counter Current in the middle part of the Atlantic Ocean (Fig 2). Its velocityvaries between 1m/s (max 1.5 m/s) in December - February and 0.5 m/s (max. 0.75 m/s in August- October.It is weaker in the east. Generally, this ocean current is hardly felt near the coastexcept near promontories.Upwelling of cold water (about 22 - 25 C) occurs especially off the coast of Ghana in August -October. Otherwise the sea temperatures vary between 27 and 29 C. The annual variation of the mean sealevel is about 0.1 to 0. 7 m near Cape Palmas in the west and the Calabar Estuary in the east. It is negligiblein the middle portion of the Bight. The waves experienced on the coast are of two distinct origins:

* the sea, generated by the local monsoon winds* the swell generated by storms in the southern part of the Atlantic Ocean.<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 169The local monsoon-generated waves come from the south-west with the wind They are generallyweaker rarely exceeding 1.25 m in height with a maximum period of 3 to 4 seconds. The storm-generatedswells occur throughout the year but become stronger during the southern hemisphere winter. The period ofthese swells vary between 8 and 20 seconds, averaging about 12 to 13 seconds. Their height in deep wateris 1 to 1.5 m as an average but occasionally heights of 9 to 3 m and above occur. They arrive from directionsbetween south and south-west. From observations made from ships in the area north of the equator and eastof 18 W and at the coast at Sekondi, Tema (Ghana) and Kpeme (Togo), it appears that waves that arerelevant to the coast have a morphologically effective wave height of 1.2 to 1.5 m with periods of 10 to 16seconds around a mean of 12 to 13 seconds The effective direction of the waves varies from N 190 - 220 Eoff Cape Palmas to N 200 - 220 E off the Niger Delta The long waves come with long crests and in trainswith periods of a few minutes.The effect of littoral transport along the coast is felt very strongly and is the main mode ofdisplacement of sand along the coast. Its direction is mainly west to east. The littoral transport of sand ismainly caused by the incessant action of waves in the Bight, in particular the Atlantic swell. Its persistencyleads to one of the highest rates of transport observed on earth .6. GENERAL COASTAL CONDITIONSThe coast in the Bight shows three distinct features:(i)(ii)(iii)The concave coast between Cape Palmas in Cote d' Ivoire and Cape Three Point in Ghana. Thewestern part of this stretch is rocky and from Fresco a Sandy beach stretches almost to the easternextremity.The coast from Shalla to west Nigeria, with a similar concave shape between Cape Three Points andthe western extremity of the Niger Delta; the Volta Delta forms an interruption The western part ofthis stretch is also rocky and sandy beaches prevail from the Volta Delta eastwards.The convex coast of the larger Niger Delta with beaches and mouths of estuaries The estuaries ofthe Cross River form its extremity.Thus there are three characteristic types of coasts in the Bight namely, the two rocky coasts, the twosandy coasts and the two delta coasts.7. THE ROCKY COASTSThe two rocky coast in Cote d' Ivoire and Ghana run practically parallel WSW - ENE. Both receivea small supply of sediments which is less than the littoral transport capacity. Thus very little sand hasaccumulated along the coast. The pleistocene ridges perpendicular to the coast, now appear as rockypromontories. The valley in between are closed by sand bars. forming lagoons in the lower parts of thevalleys. Because of the strong eastward sand transport, the short beaches fit against the eastern promontoriesand form a curved arc against and almost behind the western promontories. The process has given rise tostepped coasts. Essentially. these coasts are eroding. The strong waves hardly damage the hard Pre-Cambrianrocks, but more recession is observed at the cliffs of younger sand stones between Sassandra and Fresco inCote d' Ivoire and at a few locations along the coast of Ghana.8. THE SANDY COASTS

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 170These coasts have essentially the same origin and evolution as the rocky beaches. the f72 difference,

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 171however, is that sediment supply predominates and much more sediments have accumulated. A coastal plainhas thus formed with lagoons in the Pleistocene valleys and on the plain parallel to the coast The orientationof these coasts changes gradually from WSW - ENE in the west to WNW - ESE.The beach ridges along the coast are built by the waves up to a height of 2.5m above the mean springtide. The marshes in the lagoons are gradually silted up to the level of the highest tides. The shore is generallyflatter then along the rocky coasts. There is some equilibrium in sediment supply and loss.9. THE DELTA COASTSThese coasts have formed along the fringes of the old deltas of rivers Niger and Volta. The Nigerpresently debouches through a great number of estuaries from River Forcados to River Brass The sandsreaching the Sea are distributed along the coasts by littoral transport and form wide bands of successive beachridges Lagoons and mangrove swamps with many tidal creeks have formed behind this sandy barrier and inbetween the estuaries.These estuaries disturb the coastline depending on their sizes. Generally, an underwater delta witha shallow bar protrudes from the shoreline. The Volta debouches through a single outlet at the western sideof its delta. The greater part of its supply of .sand has been accumulating between its mouth and a pointeastward from Cape St. Paul where the littoral transport almost ceases because the south-westerly wavescannot reach this area. Heavy erosion has been occurring more north-eastward where the transport capacitypicks up again and feeds the coasts of Togo and Benin.10. CAUSES OF EROSION IN THE BIGHT OF BENINCoastal areas and, in particular, beaches are inherently unstable. Erosion and accretion occurnaturally as a result of the action of wind, waves, stream and currents and also as a consequence of humanintervention such as alteration of shorelines through the building of ports, harbours, inlet jetties, improperlysited coastal works, extraction of sand from beaches for construction and removal of vegetation from beachesand dunes. In addition to the above causes is the global sea level rise which has been estimated to be 1.5mm/year in the last century. Higher estimates have been obtained over the past few decades.More specifically the human intervention activities that have influenced coastal processes in theBight of Benin are:(i)(ii)(iii)(iv)(v)(vi)(vii)the regulation of inlets with jetties and dredging in the cases of the canal de Vride (Cote d'Ivoire) andLagos Harbour (Nigeria)the construction of large harbours with breakwaters extending into the Sea at Takoradi, Sekondi,Tema (Ghana), Lome (Togo) and Cotonou (Benin)the construction of Sea defence structures such as revetments, groynes and sea walls at variouslocationsthe extraction of sand for construction purposes at various locations as well as the supply of sand atVictoria Beach (Nigeria) to the beachdredging in some estuaries along the Bight.the construction of dams form irrigation and hydropower generation, notably the Akosombo (Ghana)and KanJi (Nigeria) damsthe extraction of gas and oil from porous reservoirs in coastal areas which lead to land subsidenceas is suspected in the Niger Delta.Significantly, it is only the coastline between Lome (Togo) and Cotonou (Benin) that presents a trueregional coastal erosion problem in that erosion at Lome affects the coast at Cotonou in neighbouring Benin;all the other erosion problems are contained within individual countries or, in the case of the Federal Republicof Nigeria, individual states.The damming of rivers results in the entrapment of sediment material from upstream in the reservoirsand also in the reduction of transport capacity of the modified flow downstream of the dam. Estimates for the

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 172Volta river after the construction of the Akosombo dam show a reduction of about 40% of the originaltransport of sand to the coast.The regulation of inlets like at Lagos and the construction of the harbours at Tema, Lome andCotonou have interrupted the littoral transport. Consequently, sand has accumulated on the western sides anderosion has occurred on the eastern sides of these structures. These processes continue and the influence ofthe works spreads along the coast in both directions. Sea defence structures such as revetments and sea wallsprevent erosion but hardy influence the littoral transport . Groynes have similar effects as harbour moles withthe effect spreading to both sides. The extraction of sand from the beaches may cause recession dependingon the quantity of abstraction compared with the supply by rivers and/or littoral transport. Short enbayedbeaches are particularly vulnerable .11. COASTAL PROTECTION IN THE BIGHT OF BENINCoastal protection measures that have been employed in the Bight have tendered to be the structuralapproach rather than a coastal zone management approach This has been the case in spite of anticipation oferosion problems precipitated by the construction of structures along the coast. The practice has been toconstruct the structures first and deal with erosion problems when they later ariseIn Ghana several coastal protection measures have been tried.These include iron sheet piling and timber sea walls at Keta, which both failed. Stone and Rubblemound groynes and revetment have been successfully employed at location like Nkotompo, Sekondi NavalBase and parts of the coast at Labadi and Tema. Due to reasons of cost, the emphasis is now on gabionrevetments and groynes These have been very effectively employed at Labadi, James Town, Teshie, Nungua,Tema, Elmina and Krokobite beaches. The use of gabions holds a great promise for coastal protection in thefuture, its greatest advantage being cost effectiveness. The table below gives a cost comparison of gabionrevetment gabion groynes and a combination of gabion/armour rock revetment structures constructed inAccra Ghana.Table 1: Comparative costs of Coastal Protection StructuresSource: Nai et al, 1993___________________________________________________________________________________Type of Length of Total AverageProject Structure coastline Project cost ofTitle Protected Cost Protecting$ 1m of coastline$____________________________________________________________________________________Labadi. GabionPhase I&II Revetment 900m 1,171,575 1,300Labadi Gabion/ArmourPhase III Rock Revetment 290m 463,490 1,600Jamestown GabionPhase I Revetment 200m 86,920 435Jamestown GabionPhase II Groynes 300m 33,650 l15_____________________________________________________________________________________Other advantages of gabion structures are that:* the technique is labour intensive requiring no or very little heavy machinery

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 173* the high porosity of the gabion structure and the low area of contact of the stones with sea wavesmakes it an efficient energy dissipating structure with good drainage characteristics* It tolerates differential settlement without fracture while increasing its structural efficiency.* its maintenance cost is low.In Togo, rock groynes and breakwaters have been employed at a few locations. At Agbodrafo, asystem of eight stone groynes of length between 60 - 110 m has been constructed A 150 m long rockbreakwater has been constructed at Anecho and another system of 4 small groynes spread over 1.5 km lengthof coastline has been constructed east of the breakwater. Benin, like Togo, has not undertaken any majorprotection works along the coast. The few structures are two rock breakwaters to the east and west of the portof Cotonou and a groyne at the port itself.An attempt to construct a system of nine groynes using concrete rings and gabion material toprotect a tourist complex failed probably due to poor design and construction.Coastal protection measures that have been employed in Nigeria are construction of groynes,revetments and sand replenishment . The table below gives erosion measures employed from 1958 to dateat Lagos Bar Beach on Victoria Island.Table 2: Erosion control Measures Applied from 1958 to dateSource: EEC Report (1989)____________________________________________________________________________________1958 Construction of a groyne at the foot of the eastern breakwater to avoid the undermining ofthe breakwater by erosion.1958-1960 Dumping of sand dredged from the commodore channel at the extremity of the easternbreakwater for dispersal along the beach by waves.1960-1968 Permanent pumping station built on the eastern breakwater supplied an average of 0.66 M3m pa of sand from the commodore channel to the beach; in between, in 1964, a zig-zagtimber groyne (palisade) running parallel to the coastline was driven in some 26 m from theshoreline.1969-1974 Some artificial sand replenishment was carried out; however, no reliable records ofquantities or frequency are available.31974-1975 3 M m of sand dumped and spread on the beach31981 2 M m of sand dumped and spread on the beach31985 3 M m of sand dumped and spread on the beach___________________________________________________________________________________In addition to the above stone revetment has been constructed at Forcados to protect oil well installations. Asandbag revetment has also been used as a temporary measure in the Forcados erosion zone.12. THE FUTURE DIRECTION OF COASTAL EROSION CONTROL IN THE BIGHTWith the identification of the causes of erosion attributable to human intervention and the increasingnumber of erosion sites being detected, it is becoming increasingly clear that a holistic approach to coastalerosion control should be the future direction of coastal protection in the Bight.In this wise, Coastal zone planning and management in which the structural approach to coastal erosioncontrol is only one of several options and may indeed be regarded as a last option should be the desiredapproach.The structures that can sustain such an approach are:

<strong>IOC</strong> <strong>Workshop</strong> Report No. 96 - Supplement 1page 174(i)(ii)(iii)(iv)(v)A coastal Zone Management Body with Co-ordination, planning, supervisory and sanctioningfunctionsA well-defined institutional arrangement for implementation of plans, monitoring and policing,research and development in the coastal zoneA legal framework to guide and facilitate the management of the coastal zoneThe development of local manpower and expertiseFinally the resources to deliver the goods.Adoption of the holistic coastal zone management approach will thus equip the sub-region to copewith coastal erosion particularly in view of global warming and sea level rise both now and in thefuture.ANNEXREFERENCESGOVT OF GHANA (1986). Coastal Erosion in Ghana Situation Report and Action Programme. Teamof Consultants on Coastal Erosion in Ghana.EEC (1989). Coastal Erosion in the Bight of Benin. Report on Expert FindingsNAI, G.G.; ANTHONIO, S.L.; and ADDO, J.A. (1990). The use of Gabions for Shore Protection.Examples from Accra. Presented at Meeting of Experts on Coastal Protection Methods,Accra, October 1990.NAI, G.G.; ADDO, J.A.; and WELLENS-MENSAH, J. (1993)<strong>UNEP</strong> (1985). Coastal Erosion in West and Central Africa. Coastal Erosion Points in Ghana andtheir Protection. Presented at <strong>Workshop</strong> on Climate Change and Its Impact on Water,Oceans, Fisheries and Coastal Zones, Accra, March 1993.